Very nice! Was not aware you could use a compact slide on a sub compact frame. Which subcompact frame size did you use(small, medium, or large)? Can you use the magazine from the compact on the subcompact frame? Thanks again for posting the pictures!
Not the OP, but you can use any 9/40/357 combination of slides and grips. Some combos may look goofy as hell (e.g. a SC slide on a FS grip) but it can be done. If goofy isn't your thing, you can always trim down the dustcover/rail end of the grip to fit a smaller frame. I have my compact grips trimmed down so that I can mount my SC slide on it, but it also still works fine with the compact slide.
Any mag larger than the mag specifically made for the grip will function just fine; you'll obviously have a gap at the base, but if you wanted to eliminate the gap - as mentioned above - you can add an X-Grip sleeve to the larger mag.
You may have to get a little more creative to, say, use a FS mag in a SC grip. But, again, it'll function just fine.
The grip OP is using is a small SC - the small SC has no rails, whereas the medium SC grip has rails. There is no large SC grip option.