318/904 to 5.9L/4 speed

The 5.9 is externally balanced engine, so, the important parts are not swap able. Motor mounts and attaching hardware from the front of the engine will swap, drivers side issue aside, the bell housing and all the clutch material would swap if it were on hand to do so.

IMO, if you can get 5 spd overdrive unit, go for it. The 4spd OD (AKA stock unit) is not very strong for performance usage. But very good for daily drivers, mild bolt on performance parts and mileage.