That is not a harmonic balancer- - - -it's either a drive flange for a marine reversing gear, or possibly an accessory drive for a piece of industrial equipment or a farm implement of some sort. Passenger cars or trucks never had that type of crankshaft snout setup, to the best of my knowledge, and I worked on lots of them in the 50's and 60's.
I'd suggest pulling the engine back out, and do at least a partial teardown to see if it's worth investing any money. If it's been sitting that long, it's probably pretty stiff, if not locked up entirely. Cylinders that have the valves open to the air collect moisture, and rust the rings to the cylinder walls.
Jerry
