The trigger's different, too, and something else but I forget what.
You mean on a Model of 1911 vs. M1911A1? Actually a bunch of things, obvious and not so obvious are different. But I'm not talking strictly about US military firearms. We could go on for pages about the changes between the Model of 1911 and the M1911A1- heat treating, finishes, shapes of hammers, grip safeties, grips, locations of markings, sights, mag releases, thumb safeties, etc
One thing I'm wondering is why so few new 1911 pattern pistols have the frame configuration (ie: no 'scallops'), and the overwhelming majority do have them. except for the short 're-issue' model Colt did a while back in which they made pistols very much like 1918 production Colts, I can think of only a couple custom pistol makers that have made the 'non-scalloped' models
It would seem to me that it is odd, given the wild popularity of the basic pistol type, that this option has not been explored
In regards to what you probably meant though, the trigger, mainspring housing (arched vs. straight), and 'flat' vs. 'scalloped' frame are the most obvious
But for this pistol type, a thing like a trigger or mainspring is a fairly simple swap. It's a little more advanced to go from a non-scalloped frame to a scalloped one