There were two different flywheels/bell housings in the Y-block era plus a lot of different transmission combos but the heavier duty one is the T-85 with or without overdrive. The Fords used several spline types in the 3-speeds since there were the T-86 and T-85 types so a person has to match the input to get a proper clutch. The early 5-bolt sbf used a 3-speed (likely a BW top loader) and the early T-10 4-speed so the inputs can be different. Some may cross over but not all. Later 6-bolt small blocks used some T-10, super T-10, and some Ford top loader 4-speed types. The 3-speed manuals were dying out so I don't know how long they lasted into the 60s.
There is some similarity between the T-85 and the early T-10 so some stuff could cross over there. There may have been a Dagenham UK built 3-speed also used on SBFs but I don't know much about them. They were likely for 6-cylinder cars.