The USGI rear cartridge stop will work with all calibers, but it creates some challenges with 308. It requires the rounds to barely be seated in the links to clear the stop. I have not tried 8mm yet, but I recommend that if you want to be able to use 308 in your gun, use the smaller Israeli stop.
I have done some experimenting with an all-USGI build, to see how well 308 can be made to work. What I found was that the 30-06 belt holding and feed pawls, which the Israelis redesigned, actually work just fine in 308. But that right rear cartridge stop sticks out too far forward to work easily with the shorter round. With the shorter Izzy stop, you can use all other USGI parts reliably. Of course, this does require the two LEFT side Israeli cartridge spacers, front and rear.