Why not just look for a M25 chambered in .45 Colt? Your revolver dates to 1962, if it's in good or better finish, no way would I go reboring, honing, etc. the cylinder bores and ruining whatever collectability it has.
.45 Colt has thinner case rims than .45 Auto Rim, so there would be a slightly wider gap on your cylinder between it and the recoil shield. The Colt cases might have issues with intermittent FTF because of light strikes from the extra slight distance the firing pin has to move to properly punch the primer, and the cartridges would have a bit of room to move back and forth in the chamber.
.45 Colt rims measure 0.060", .45 Auto Rim measures 0.090".
If you can find a .45 Colt "short cylinder", you maybe could swap them out, but the standard .45 Colt cylinder is longer than the .45Auto cylinder and you'd need to recut the forcing cone, which would then make .45 Auto cylinder too shorter to work in the gun. Here is my M25-5, which is factory chambered for .45 Colt. Look carefully at the length of the cylinder and the space between the rear of the cylinder and the recoil shield.