Hy lastchancetowing, the small block Chev V8 was available in the truck chassis starting with the 55B or second series, the vendors sell a kit for the front engine mounts which can be bolted to the chassis front crossmember allowing you to install the V8 engine the same way the factory did. As for automatic transmissions the only one that was available from the factory was the dual range four speed Hydramatic, these are the "stock" options. If you don't mind some fabrication the possibilities are just about endless, hope that helps.
