The big trucks that used the 337 could be had with a 5-sp synchro trans, with either O/D 5th or direct drive. They are hard to find now, and weigh at least 300 lbs. I think you are better off adapting to something more modern.
Obviously a 'heavy' one.What type of 'hot rod' is the 337 destined for?

In the mid 50's a friend of mine put a 337 in a`41 Ford Convertible. From what I can remember it ran very well.