I'm not familiar with the AW71. I better look it up. Could be interesting. Twice as good as a 35 +1?
They were used in lockup and non lockup in 760s, 740ts, then 940s and late 240s. A 4 speed version of the bw55.
^ This.

And they are twice as good as a BW35 ... with a +1 extra gear (overdrive).
4 years later

Hey mate.. I've got a good motor in Perth

The othe bottom end knock could be bearings or even a bocken cam plate. B20s are tought as nails. Rip it out. Rip it apart and find out what's wrong.