Hi
6a and 9a are what are known as 'bubble blocks', The same height as the kr motor but with bulges in the crankcase area to accommodate the longer throw crank to get 2L from 1.8L hence the 'bubble'
ACE and Abf are the tall block motors (290 mm Tall with 8mm longer conrods) The ABF is 150 hp and the ACE 140hp as you have said due to the milder cam.

I have a 6a motor in my Audi 80, it has 2.0 stamped on the rear. I will see if I have any pics of the rear of the block and post up so you can compare.