Are these decent shooters?
What is a fair price to pay for one these days?
From what I can find, these were made of new production cast stainless parts in the 80s.
Can parts be replaced with .mil surplus if needed? is there anything to watch out for?

The Stainless Steel Carbines

From 1978 through 1984 all of the Iver Johnson carbine models were offered in a stainless steel version. All of the stainless steel carbines were manufactured in Middlesex, NJ between 1978 and 1982. Those sold by Iver Johnson after the company moved to Arkansas in 1983 have the markings of Middlesex, NJ with the letter A added to the end of the serial number. One stainless steel carbine manufactured during 1991 and mounted in a commemorative Stars and Stripes stock has been observed, the serial number beginning with the AA prefix instead of the standard SS used for stainless steel. This was likely part of the inventory clearance in the company's final days.

All of the receivers, slides, bolts and trigger housings in stainless steel were made by investment casting. All of the parts are interchangeable with their blued steel equivalents and surplus GI parts.

The stainless steel carbines manufactured by Iver Johnson of Middlesex, NJ have been one of the most durable commercial carbines made to date. They generally have been superior in quality to the stainless steel carbines made by Universal Firearms and sold by Iver Johnson 1985-1986. Further details on the stainless steel carbines manufactured by Universal Firearms and sold by Iver Johnson can be found on the page devoted to Universal Firearms.

What You Need to Know About Parts

There is only one standard for the dimensions, machining, quality, and life span of every part on an M1 Carbine. The standard adopted by U.S. Army Ordnance for the U.S. .30 caliber carbines M1, M1A1, M2, and T3. There is no other standard. Ordnance standards were established based on research and development, testing, field use of the carbines during WWII, and more. These standards insured the parts were interchangeable between all of the U.S. GI carbines, regardless of manufacturer. They also set the requirements each part would have to meet to pass inspection, not only by the manufacturer but also by U.S. Army Ordnance inspectors assigned to the manufacturing facilities of each of the primary contractors making carbines. If a manufacturer didn't get it right, it didn't go out the door on a finished carbine. If a manufacturer consistently and repeatedly didn't get it right they risked losing their contract.

Almost all of the post war commercial carbine manufacturers started out using as many of the surplus GI carbine parts as they could get. As the availability of each part dried up, each commercial manufacturer made, or subcontracted to be made, a commercially manufactured part that would fill the role of it's GI counterpart. While these commercially manufactured parts may have been dimensionally the same as a GI part, none of them were manufactured using the standards established by U.S. Army Ordnance. The new "standard" became whatever "worked" and was cost efficient. How well it worked and for how long was/is nowhere near the quality and lifespan of any of the parts manufactured for U.S. Ordnance. Commercial manufacturers could get by with parts that didn't meet the standards of U.S. Ordnance as their carbines were mostly made for the average citizen during peace time, not soldiers subjecting their carbines to conditions common during a war.

If a commercial carbine and it's parts were manufactured to GI dimensions, then they were "GI compatible", meaning they could be interchanged with all other parts manufactured to GI dimensions, including the surplus GI parts. Most, but not all, commercial carbine manufacturers attempted to stick to these dimensions and interchangeability. Some did it better than others.

Buying a Replacement Part

The first thing you need to determine is if the part you want to replace is "GI compatible". The table below lists the commercial carbine manufacturers and identifies which ones made carbines that have "GI compatible" parts.

If a carbine is indicated as less than 100% "GI compatible", read the web page for that particular manufacturer.

If a carbine and it's parts are GI compatible, the best replacement part is one that was manufactured for U.S. Army Ordnance (surplus GI parts-see bottom of page). There are plenty still available and still in very good condition with many years of service left in them. If the cost is above what you want to pay for a part, the commercially manufactured parts are an option. Realize the quality control standards are an unknown. Most GI compatible parts will work. The questions is, how well and for how long. Most parts will wear out quicker and need to be replaced sooner than their GI equivalent would.

The following parts should be inspected occasionally and replaced before the wear becomes excessive. Parts followed by an asterisk (*) are safety critical parts you should seriously consider replacing with GI surplus parts instead of their commercial equivalents if your carbine's parts are GI compatible. A few commercial companies may have manufactured and hardened them to the high standards necessary for safety. The problem is knowing which commercial manufacture did and how to identify their parts from those who didn't. The markings used by U.S. Ordnance contracted companies for quality control served a purpose. Commercial equivalents rarely have identifiable markings. Testing each part requires equipment and expertise that is cost prohibitive.

   Bolt*
   Firing pin
   Extractor
   Extractor spring and plunger
   Hammer*
   Sear*
   Slide*

Where do I buy the parts I need?

I do not endorse retailers. There are plenty of other retailers, just do an internet search on what you want to buy and shop around. Gunbroker.com is an auction website with hundreds of sellers offering just about any part you would need. Like any other internet auction website, common sense and caution when dealing with people you don't know is advised. On the links page there are links to parts suppliers I have found to be honest and reliable.

http://www.m1carbinesinc.com/carbine_Ij02b.html

Fair is in the eye of the purchaser right now, but you can get an idea from Gunbroker.  A GI compatible carbine in good condition should go $800 or up in my AO @ the moment.  @Commando223 just sold a late Universal non-GI compatible for north of $500.

I owned a factory IJ M-2..... and it was nothing but trouble until I essentially replaced every part but the registered receiver with USGI.

The biggest issue was the machining of the channels on the bbl that the bolt carrier ran in.....they were so far out of spec, the carrier would jump out of it's track in the receiver every few rounds....

You have a 50/50 chance of getting a good one.... The early Plainfield and Universal guns are actually better bets

Thanks for all the info.
Are the Stainless carbines that came out of the jersey factory considered to be part of the “early” good years, or “late” problematic years?

Late.  Came after Iver Johnson bought Plainfield.

http://www.m1carbinesinc.com/carbine_ij.html

The Stainless Steel models command a higher price than normal model due to their rarity. IIRR only 5000 were made and they were popular with boat owners due to the SS nature.

I know of 1 person who owns one, he's never complained about it outside of having issues with cheap mags.

The last one I saw listed on Gunbroker went for around $1300 per current panic, too high IMO when you can get decent Plainfield's cheaper.

I've owned 1 IJ over the years, it was a decent shooter but mag picky.