Same clip is used for both rounds.
The magazine block that is installed in some Garands that have been converted to 7.62 NATO/.308 are to prevent the inadvertant loading of 30-06 ammo. The enbloc clips only fit in the magazine in one location, they wont lock into the rifle if not positioned properly. Actually they may not even enter the magazine well if not located properly.
Wait a minute....
OK I'm back. I just pulled one of my Garands out of the safe and tried to put a clip of 308 ammo in any way but right. It's a no-go on that one. The mag block is purely to prevent loading 30-06 in a 308 chambered rifle.
Hope this helps.
BTW, the mag block goes in the front of the mag well, not the back.
Don in Ohio