I used to have a model R6600 A2 HBAR which I bought back in 1986 brand new with small FCG pins and large pivot pin.
There are super rare pre ban Colt rifles with both small FCG pins and small pivot pin, an ARFCOM staff member and collector posted a picture of his rifle either before or after he sold it, he posted it here in the Colt industry forum sometime around 2005 - 2006.
I agree what these other guys said just get a new 6601 with small trigger-hammer pins, make sure you touch and feel it first to be sure you got the small pins before buying it.
I have never seen a new 6601 locally, at least not since before the AWB expired. I'd probably be buying from Bud's Gun shop and having it sent in. Is there a real chance that those rifles are NOS large holes?
There is always a good chance that some new 6601 could be NOS, make sure your dealer knows that you wanted specifically a brand new (not NOS) rifle with the small FCG pins because you're going to install your Geissele small pins trigger group on it.
When I bought my new 6721 A3 carbine last March, I told my dealer I wanted to get the new model with the small FCG pins and I also told them that if it didn't when I picked it up that I won't take it, and my dealer agreed to exchange it if it didn't have the size of hole that I wanted.
I even talked to my dealer's distributor and ask them if what they're selling are NOS and the distributor told me that what they got they recently received from the factory.
When I actually got my 6721 at the dealer, I opened the factory paper tape seal of the box and I immediately compated the FCG pins with a spare small pin that I brought with me, and it was small pins indeed.
When I got home and took apart the handguard to see the mfg. date on the barrel I was surprised that the barrel and the birth plastic bag had the same date of 05/ 09, it was made 10 months before I got it and it already have small pins.
I was also planning of changing my trigger with the Geissele SSA small pin, because the small pin version is cheaper than the large 0.170" version, but when I tried the trigger on my new carbine, the trigger is excellent, light and smooth similar to the Geissele so I don't need to upgrade it, I'll just use my factory trigger.
Bottom line is tell your dealer exactly what you want and have him agree for an exchange in case you got something you don't want.