Ugh, this is all coming back to me now. There is a config prom on the two controllers "CORVUS01" is the 8" (which is a 1791) and "CORVUS02" is the buffered (upd765) 5/8 could be supported on both, but I've only seen 5" on buffered controllers.
I guess I need to check if there was a special EPROM for the flat cable cards in the Concept.