Refer to the Ford Parts Price List of July 1, 1931 of which a reprint is available is available from the major "A" parts dealers. The cowl tanks are listed on Page 22:
A-9002-A 1928-'29;
A-9002-B 1930;
A-9002-C 1930-'31;
A-9002-E 1931.
What follows I read somewhere, but I cannot recall where.
The A-9002-A Cowl Tank of 1928-'29, although it looks the same it differs from the A-9002-B Cowl Tank of 1930. In 1930, trucks used leftover 1928-'29 82-A Cab Assemblies, so the tanks look the same but the gas cap fittings are different. The 1928-'29 A-9002-A Cowl Tank has a threaded gas cap fitting that fits the 1928-'29 threaded A-9030-A Gas Cap. The 1930 A-9002-B Cowl Tank is a 1928-'29 Cowl Tank that has a bayonet twist-on gas cap fitting that accommodates the stainless steel 1930-'31 A-9030-C Gas Cap. In summary, the 1930 A-9002-B Cowl Tank is an oddball that was used in trucks. The 82-B Cab Assembly replaced the 82-A Cab, and the 82-B Cab has the A-9002-C Cowl Tank. All 1930-'31 cars also have the A-9002-C Cowl Tank until in 1931, when the gas shutoff valve was relocated onto the engine side of the firewall. This brought about the production of the A-9002-E Cowl Tank that has a unique gas outlet fitting which accommodates the indented firewall in cars and trucks.
By the way, I left the "R" off of the part numbers because it means that part was carried in stock for service after its production line usage was discontinued.
I now have a headache!