wiper motor /washer question

[1963c-10]

Trying to convert my single speed wiper to the two speed w/washer. All of my research shows that 63-72 are interchangeable. The question is what are the difference in the 60-62 motors that wont allow them to interchange with a 63? They use the same switches, transmission arms, wiper heads/arms, so why wouldn't they fit a 63? Any help would be great. I have the switch, bottle, bracket and nozzles (already were on truck, but none of the other stuff was), so im looking for the motor/washer assembly. Have found a unit on a 62, but I dont know that it'll work.