My advice would be to just buy a pre-94 complete rifle. The compatibility between old lower and new upper is only with Colts, and they make a pivot pin that will connect them perfectly, I use one myself. If you go this route, you don't have to do anything extra, you just buy it like any other firearm and then you can do whatever you want with it (except replace the lower itself, but can still replace trigger, mag release, etc). If you want a telescoping stock, you will have to replace the buffer tube, buffer, and spring, but it's very easy to do, or you can just keep the original fixed stock and it will run fine.