The right angle adapter for the 6100/DOS is specifically for the DOS card. It's not the same as the adapter for video cards - it apparently re-creates an '040 PDS, meaning Quadra DOS cards can be used in 6100s and vice versa. Thus the G3 upgrade won't work with the 6100 DOS card either.
But wait... if this DOS card really does go in the 8100 PDS (which the box should say, somewhere), maybe it *would* work, at least with a real 6100 PDS RA adapter.
That haul is possibly the most awesome MLA thrift score evar.