Hi,
I just had my 1000's auto box rebuilt and the difference between the "a" and "b" is that the "a" has a notoriously weak diaphragm spring on the first clutch which was strengthened for the "b" boxes. Mine was broken into three peices and it cost me $600 to get a chrysler torqueflyte one machined to fit! total cost of the auto trans rebuild due to damage from a neways additive: $1250.00.

But the auto rebuild bloke recons that these are still one of the best auto's around!