4 speed flywheel

You will need a 360 flywheel the 360 is external balance, and the 340 is neutral balance, so the flywheels are different , I bought one from 440 source for $99 it has removable weights so it will work with both internal, and neutral balance.

Not 100% correct, the apr.1, 1972 the 340 became external balance so there is a 340 external balance flywheel. Just putting that out there.