Why not do it like General Motors did it in 1955. A 1955 and later transmission and rear from a 1955 and later will have will have an open drive shaft. But remember that the torque tube kept the rear axle from torquing and the axle seats were hinged. Either weld the hinges tight or fabricate axle seats or modify some from a trailer. Just make sure you keep the same pinion inclination angle. From your first post it sounds like you have a rear that will work. A 1955 or later pickup or passenger transmission will work.