Just got my Sistema 1927's today.

Never owned a 1911 or clone before, and I've got to say, I'm loving these guns.

Question, though - one of them has a spring-loaded mag release, which I really like.

The other doesn't, or is malfunctioning.  Can someone point me to a 1911 armorer's guide or something that can explain takedown of these, and how to resolve this situation?

Also, where's my best bet for some more magazines for these?

When I'm looking at accessories, am I looking for "1911 Government Model" or what?

check out Here for disasembley

and CDNN for mags and accessories

When I'm looking at accessories, am I looking for "1911 Government Model" ....?

.....YES

Alrighty - another newbie question - what's this 70 series, 80 series, etc?

More than likely, they are the equivalent of a 70 series.

Quoted: Alrighty - another newbie question - what's this 70 series, 80 series, etc?

80 series pistols incorporate an extra passive safety mechanism while 70 series do not.

In the 1980's Colt introduced a new series of all their models, with an additional safety device, namely a firing pin safety, which didn't allow the pistol to fire if the trigger wasn't pulled to the end of its travel. The guns produced there after, are called Colt MKIV - Series 80. This safety system, although it was deemed necessary in today's world of lawsuits, it had a bad effect on trigger pull. For this reason, it was never widely accepted by shooters who want a decent trigger pull on their firearms. This same firepin safety mechanism is also used in the high-capacity pistols, produced by Para Ordnance. m1911.org

Kimber came out with a different safety system which they deem a series II safety. It is disengaged when the grip safety is fully depressed.

Your Sistemas have neither of these "features"

Jonathan