Kkirkup, you don't have to drill a hole in the frame and fit a pin. You can do as I have on a couple of my guns and just epoxy some kind of a stop in the bottom rear of the grip. It will lock the grip in position and it's much easier than the drilling the pin thing. I'm trying to get a picture right now, hang on. Ok, got it! This is a Bounty Hunter .22 that came with one piece grips. I removed them and installed a pair of Colt-clone grips. Rather than drill the pin hole, I epoxied a nylon nut onto the grip (with it in position) to hold it from shifting on the gripframe. My quick fix here is not very neat, but it does do the job well. Be sure you choose something that the epoxy will hold (my first attempt with a small piece of plastic did not). If you want a nice, tight fit, you can try it on the gun, then remove and push it just a little more to the rear corner of the grip. When the epoxy dries, you need to file the piece a little to get it onto the gun. That will give you a nice fit. Good luck with it. 44 Man.
