904 differences

There were many updates and changes on the 904 style trans over the years. Some involve the size of the input shaft and number of seal rings. Also the size of the seal ring on the rear clutch drum that goes into the reaction shaft. The way the back of the reaction shaft was machined to accept the 5 disc clutch drum and the length of the splines on the rear clutch drum to engage the 5 disc front drum.

There were also changes made to the case for the suction side of the pump and of course the pump as well. But to answer your initial question the main difference between the pre 72 and the 72 and up transmissions was the rear seal size and the kickdown servo bore size.