Hi Msgfox,
There are several calibers that you can put into the 1911 frame.
45 acp,
9 mm,
38 Super ( Almost 357 mag specs)
40 s&w,
Just about anything that fits into the 1911 magazine without binding.
I have been thinking of a 7.62x25 but I will not be able to use factory ammo as it is too long. Handloads only
The big issue will be the slide and ejector, You will need to get a complete top end unit for each case head size and the appropriate ejector. I think that the 38 super is the one you want and is easily done. Just remember that the the point of aim will change if you keep the same slide and just change the barrel.
Also don't forget the magazines will be different for each caliber as well.
Paul