In 1931 Ford offered a factory option to install the Model AA Ford truck four speed transmission in a Model A chassis on special order.
This offering was documented in the July 8, 1931 Indianapolis Branch Dealer Service Letter above, as well as the 1950 edition of the Ford "green bible" Chassis Parts Book, as used by dealership service parts departments.
Typically the four speed trans is found on pickup trucks, though the 1931 Branch Service Letters do not indicate any restriction on which models Ford would install it in. It is possible other people such as rural route mailmen ordered it in coupes and tudors.
Pictured above is the Ford drawing for the A-7085-E transmission rear bearing retainer which was released in 1931 for special equipment use on the 4 speed Model AA transmission when mounted in a Model A chassis.
This retainer appears similar to the typical AA-7085-B retainer below, however it is smaller (one inch total thickness) and is the proper retainer for use in a Model A chassis. (also note the A prefix part number on the drawing, not AA).
Pictured above is one side of the typical AA-7085-B rear bearing retainer used in 1931 in the Model AA Ford truck chassis. This retainer has an overall total thickness of 1.375 inch and is too thick for use in the Model A chassis.
Pictured above is the opposite side of the AA-7085-B retainer as used in a Model AA truck chassis. Note the AA-7085-B part number cast-in.
Pictured above is the Ford drawing for the A-7092-D universal joint front knuckle, which was released in 1931 as part of the A-7090-C universal joint assembly for special equipment use (see note in lower left) on the 4 speed Model AA truck transmission, when mounted in a Model A chassis.
This knuckle is similar but different to the 81C-7090 universal joint used on the 1938 Ford pickup with four speed truck transmission (which was essentially the same transmission as the AA, except for the case).
The A-7090-C universal joint assembly has the A-7092-D (AA 10-spline) knuckle on the front and the typical Model A 6-spline driveshaft knuckle on the rear.