OK this might be a stupid question but thats never stoped me before. If you have acouple D2's that are the same year what are the main differences between the 3j,5j,4u&5u.I know there are many in the engine and pony motor but what about the undercarrige ,the rollers, sprocket, chains ? or the final drive, steering gears,brake drums. are there parts you can swap from one to the other to make it work? I know I think too much.