I've never heard of a true "drop in" replacement barrel for a 1911..
Maybe because you never worked in an Army Forward Support Company.
I can tell you with absolute certainly that GI barrels, (and virtually all other parts) when replaced were "drop in fit". No work was done And I would be surprised if any ever was. If, in the RARE case a part did not drop in fit AND work, it was tossed and another part (that would fit and work) was installed.
And it worked that way with all the other weapons, as well. The only time any work was done to fit a part, in any of the shops I worked in was literally when there were no other parts available (which sometimes happened with the mortars).
This is probably a bit of an overstatement, as I'm sure a repairman or three would take a few file strokes or stone something, did it myself, but in general, parts were not fitted. It went in the gun, and the gun passed its function check, and went out the door when the customer unit picked it up.
Needing to fit a barrel to a 1911 in order to have it work comes from the over tight match gun mentality prevailing in the civilian world today.