Do I have the right harmonic balancer?

yes if the balancer says "for internally balanced" that means the damper is neutral (ie. in balance to itself) so it would not add any balance to the crank. same as a flexplate or a flywheel, they are all neutral balanced ( in balance) so if you add a bunch of 0 balance parts, flexplate, flywheel, damper...you still got a 0 added balance to the crank. This made assembling motors easier as everything past the crank was the same 0 balance. the cast 340 and 360 were spun up on a balancer when assembled (Detroit balanced) and the balance was obtained in the damper that would also be considered a balancer on these cast crank motors.