You know, if our laws weren't so strict up here in Canada (no airsofts allowed across the border) I'd be willing to buy a couple of these off eBay myself and do the same thing.
Definately a good idea there, Ithica. And a good choice as the base for the Pistol. Regarding the magazine, when you get these in hand check to see what the internal construction of that area is.
See, on my Tokyo Marui Sig Sauer Polizei P228 airsoft pistol, when I remove the magazine and look into that internal compartment I can see that the rear of the grip is just thick ABS plastic, and is separate from the magazine mechanism (the magazine is actually held in a casing, apart from the grip itself).
If yours is the same in that respect, then you should be able to simply cut off that "excess" plastic on the back of the grip until you get to the casing for the magazine release, which will then give you the correct angle and look to your grip.
Of course, if none of what I said above made
any sense (it's easier to show than explain, lol) let me know and I'll explain further
