My opinion is: if you can swap the tranny for a 5 speed, go for it.
2,8 often used zf 3 hp 20 like 2500(this is what I know)....euro version with long wheel base used BW65 ....I think the 3hp20 cannot be mated to the torque and power of a 3.0 engine....
so check what kind and brand of auto gearbox you have....
regards, from Italy
Francesco