Im not real sure about the "A" or"B" models but when I worked on the 3700s at a local ski area back in the 70's the first 3700 we got with the 670I allis Chalmers engine had a separate 12 volt motor to release the Osco brakes , Allis Chalmers injectors in the engine, and a Funk gearbox for the 2 sundstrand drive pumps. Shortly after on the second 3700 that was bought still using the allis Chalmers 670I engine they went to Bosch injectors so they could bring the pressure up on the injectors to 6200, from the 5500 that the AC injectors were capable of. They also removed 4 stacks of springs in the Osco brakes so they could run them off the sundstrand pumps, doing away with the 12 volt pump setup. Also about this time the tillers started appearing so thiokol started using a funk splitter box that three pumps could bolt to so that there was another drive pump available to run the tiller. My belief was when they started with the 3 unit funks for the tiller was when they called it the 3700B. I know when they started putting the cat 3208 , 250 H.P. engine in they were called the 3700C. Just a note even with the best service, oil change at 100 hrs, we seldom got over 3000 hours on the AC machines before engine failure, they were just trying to get to much horsepower out of engines that were designed to produce 140-160 H.P. (JMO) the engines had crankshaft failures, not bearing failures.