Had to do with the clutch springs AA were heavier than the car and then Ford went to the same springs on all hence A and then went back to AA on the trucks?????
I have had decent luck with Howells many have not. Only buy from them at a meet. They use to be there but has been several years since I have been. Never order from them only buy direct.
Dearborn(Rouge) used f, fd, b, c and d in the body #s. Get Steve Plucker's book on the assembly plants and production of the Model A. What is your gas tank #?