This guy says 55-57 , I don't think he really has a clue.
55-56 would be neutral balanced , 57 would be offset.
Lots of holes drilled on one side. Maybe offset ? Maybe just poorly balanced wheel ?

http://www.ebay.com/itm/Oldsmobile-C...dWO4GY&vxp=mtr

 

I would not think it to be NOS with it being aluminum. Probably aftermarket. Weren't 57-58 balanced with add on weights rather than drilled or Am I thinking flex plates here?... Tedd

 

The factory synchromesh flywheel part numbers were:

564281 for 1954-56

568944 for 1957-59

So, they were different, but I don't remember what the difference was.

 

I haven't seen many stick type flywheels for those year Old's( most are automatics) but all I can remember were steel....Tedd

 

Yes, the shop manual says that it was of cast iron with a hardened steel ring gear shrunk on to its outside diameter, so the aluminum one would be an aftermarket. It also said that the synchromesh flywheel used longer mounting bolts than the one for the Hydra-Matic.