This may just be pie in the sky thoughts but. Could anyone add any input? I have a 25-5 with over sized cylinder bores (.458) while this has never proved to me to be a problem I am now thinking it may be nice to have the correct size installed .452 (S&W will do this for about $160.00) which is OK, but at the same time I would like a cylinder fitted for .45 ACP which S&W will not do, unless I only want an ACP gun. Does anyone have any thoughts on how I could have both?

Setting up a Smith for both .45 ACP and .45 Colt is problematic due to the two cartridges requiring very different headspace. The ACP/AR cylinder is somewhat shorter at the rear to make space for the clips or AR rims. If the frame lug is of such dimension as to allow use of the .45 Colt, you'll wind up with an ACP cylinder that will move back & forth about .060" in the open position. This, combined with the clearances required for smooth operation, could mean that the ACP cyl. could actually fall out of the gun during extraction.
A .455 Smith that has been counterbored and deepened for .45 Colt will usually still fire .455 safely (if perhaps inaccurately) because the cylinder length hasn't been changed. The 2-cyl. setup for Colt/ACP doesn't usually work out well, IMHO.

Larry

Alternatively, you could have S&W install the 45 colt cylinder, then send it to someone like Pinnacle or TK Custom and have it machined to take moonclips.

The process leaves a slight rim around the outside edge of the cylinder which allows 45 colt cartridges to headspace correctly. The moonclips sit in a recess which allows the 45 ACP to headspace correctly and the cylinder to close and rotate without binding. You cannot use 45 AR with this conversion.

Some folks say the extra jump the ACP has to make to the cylinder throat has a negative effect on accuracy. I have a 625-9 mountain gun with a machined cylinder and I've never noticed an accuracy difference (so long as I remember to adjust the sights correctly for the change in projectile weight).