I think you need a 1954/55 Chevrolet 235 engine or GMC 248 (6 Volt) to work or you need a 270 or 302 GMC engine (The 302's all came with the 6 bolt flywheel). GMC made a 6 hole flywheel for the 6 volt but they are hard to find, you will have to go to a 12 volt flywheel and starter.
What year hydra-matic do you have? Is it complete?
old Post old post 2 There are several HM guys on board.