With your 51 truck the bellhousing is the key piece, really beefy side mounts and modern trany pattern. Any 235 or 261 ci six will bolt right up as well as any modern trans, Muncy, Saginaw or T-5(with minor mods) etc etc. What would be ideal for you is to locate a 55 and later pickup for the trans, rear end and possibly even the drive shaft. To go open drive you can't use any of your stock parts back of the bellhousing.
