[WhoKnowsWho]

How dificult is it to change calibers in this version? New slide, new barrel = about a new gun right?

[hksw]

And new mag. If changing to/from .357 mag, new recoil springs.

[SDC]

The later versions were designed from the start to be quickly interchangeable, but the MkVII wasn't; provided you can find an early set of parts, you should be able to swap them over fairly easily. One thing to watch for; since the MkVII gas plug/piston isn't permanently attached, I've seen a LOT of them installed incorrectly, and this ends up battering the piece to uselessness. HTH.