"From what I've read there's no real adapting needed to mix and match the frames and slides... you could well toss a SC slide/barrel onto a compact frame and go for it."
You are right....up to a point. The SC slide (and barrel, of course) are shorter than the C (slide and barrel). So, the (front end of the) C grip frame will be too long for the SC slide (to be flush with the end of the slide). So, I would need to shorten the front end of the C frame. That is what I meant by "adapt".
Certainly, from a purely functional point of view, most any of the barrel/ slide combinations can be assembled onto any of the grip frames (and function just fine), I believe. However, they may not look correct, in some cases.
At any rate, I probably won't get an SC kit for this, after all. I have no interest (unlike many P250 owners) in changing calibers.....so it seems a waste of money now. What I WILL probably do is get a spare C size grip frame, remove the rail.....and do a custom paint job on it. Then, just swap in my FCG, barrel and slide assembly. Then, I might similarly modify the original grip frame, only with a different look.