So I am attempting to put a short 45acp slide and barrel on this 10mm long slide pistol ... right away I note the ejector is wider than the slot in the slide. I think this is because the 10mm long slide version calls for a beefier ejector. Looks like I have to mill out the slot in the slide or switch out the ejector. Which is not ideal because it's tricky to switch that out every time you switch calibers. Anyone been down this path?

no rem1911 experience but I do have an Auto Ord POS cast frame that I switch to every caliber ever made. It was originally 45. I always change the ejector among the different rim sizes.

10/40/357 is the same
38 is shorter than 9mm.
and 45.

That makes sense, will contact Rem to get the parts.

You would be much better off getting parts form Egw, or one of the other quality manufacturers. Brownells stocks most