Sorry, didn't see your post, we must have posted at the same time. A lot of early 100 cars I've seen have the one piece intake NF motor, BTDT many times. I also agree with late 2.3 5k you list as well.
Yeah, looking at the time it shows a 1min difference....I didn't see your post until later either.
Anyway, the 100's were supposed to all get the NG style head, but typical Audi, there are probably some/most early cars that still use the true NF head while Audi was using up stock. Kinda like some MC-2's coming with a K26 bolted on the EM.