The vast majority have a ten-round fixed magazine, loaded through the top via stripper clips. There's a guide slot for the clips at the front of the bolt carrier. The SKS-D and SKS-M models were modified to accept detachable AK-47 mags.
I’m pretty sure the enbloc 8-round clip for the Garand would be interpreted as a “detachable ammunition feeding device”.
Unlikely. The "feeding device" (spring-loaded follower) is integral with the rifle. Of course, that's not to say that BATFE won't come up with some new and astonishingly stupid rule.
LOL, active 2A minds think alike!