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 #?
My Uncle who was a Ford Mechanic from Model Ts to 70's. Once told me he used a 2x4 and shut the door. He said if a customer saw how they had to fix things they would never come back, but it worked and the customer was pleased. Tricks of the trade
Only buy from Howells when they are at a swap meet and only buy simple parts. I bought the under seat part for a 1926 roadster fit well. But at a meet you can carry the part home