If your truck has a torque tube its going to be more work than it may be worth to adapt something like a T-5. I'm sure it could be done, but it might require a smart fabricator and machinist.
Patrick's used to offer a kit that put a Saginaw 4-speed in a torque tube AD. While its not OD, it is fully synchomesh and more pleasant to drive. I have no idea if that kit would work on a '41 3/4-ton.
