I guess the title says it all, I have been wondering for a while now about which currently produced 1911 pistol best replicates the standard government-issued 1911's?  In essence, do most of the new pistols match part-for-part with the original's?  Can all parts be interchanged?  I am interested in the Springfield G.I. model, as I want one like "grandpa used to carry".  

Thanks for the help.

Probably the 1911's that's most closely match the original USGI 1911,s are the Colt 1991-A1 and the Springfield "GI 45".

The original specs for the 1911 were Colt's specs, the government adopted Colt's specs unchanged, and all other USGI suppliers toed the line and slavishly followed those specs, or they weren't a government supplier.

Most makers have drifted somewhat from the original specs since they don't have to follow them, and although most parts will still interchange, they often will need some fitting.

Most new 1911's use a lot of cast steel and MIM (Metal Injection Molding) parts.  Colt has gone BACK to using more and more forged parts, and has pretty well stopped using MIM.

The Colt IS the original USGI pistol, and they've made it with only minor changes since 1912.
It's made of largely forged and milled steel, just like it always was.

The Springfield uses some MIM parts, some cast parts, and I "think" a two-piece barrel, which is NOT as good.

Whether it makes any differnce to you, the Colt is still made in Hartford, the Springfield is made in South America and finished here.

The Colt and Springfield will LOOK more or less like a GI 1911, and almost all parts will interchange, possibly with some fitting on the Springfield.  
They aren't going to be exactly like a GI issue, but close enough "for government work".

Quoted: . . the Springfield is made in South America and finished here.

From what I understand, SA has a long-time manufacturing relationship with Imbel of Brazil.  Imbel made the SAR48/SAR4800 FAL-clones for SA in the late 1980s and early 1990s before GWB Sr. banned them.