I realize that the vast majority of new parts require fitting, some of it pretty extensive.

I've been learning a bit more about working on 1911s from my father. He was an armorer in the Marine Corps for a number of years and has a ton of GI parts. He gave me "a few" parts, which turned out to be enough for about 7 complete guns.

Anyway, I was messing around with some part swapping with some GI parts on one of my practice guns and noticed that aside from the sear and disconnector, none of the parts require fitting to function(although replacing the hammer did increase the trigger pull by a couple of pounds).

Anyway, back to the question. Does anyone know if GI parts are designed to drop in easily instead of being fitted, or is it just coincidence?

Quoted: I realize that the vast majority of new parts require fitting, some of it pretty extensive. I've been learning a bit more about working on 1911s from my father. He was an armorer in the Marine Corps for a number of years and has a ton of GI parts. He gave me "a few" parts, which turned out to be enough for about 7 complete guns. Anyway, I was messing around with some part swapping with some GI parts on one of my practice guns and noticed that aside from the sear and disconnector, none of the parts require fitting to function(although replacing the hammer did increase the trigger pull by a couple of pounds). Anyway, back to the question. Does anyone know if GI parts are designed to drop in easily instead of being fitted, or is it just coincidence?

GI parts are always supposed to be universal.  On a GI 1911A1 all the parts should go together without any special fitting.