Hi Guys
the bits that are interchangeable without mods are the twist grip and foot pegs
You can graft a head and barrel on a TM250 only (if you do it right) with considerable modification to the left transfer on the crank case.
If there is going to be a replica frame made it will need to be a good one.
The 74 was not an available to everyone bike and was issued to secected race teams who paid a truck load of money to own them, the one I own was ex team Phil Thew Suzuki Randy Jone's bike the RN400 was Geoff Worrels Suzuki Australia bike but the 75 RH was a pre production RM250 in a lot of ways with an RH engine # rh250000400 and on and the sand cast bits left over from the 74 bike. Interestingly if you get a really early RM250 / 370 you may get it with a sand cast rear backing plate with RH part numbers on it, this was Suzuki using up the bits as well.
The RH was way ahead of the TM and I could go on forever on the subject but make this last point, the clutch on my RN400 is a sand cast unit and is the same bit that was on the real works 370 so developed around say 70/71 the closest I have found to it is the one out of the RM400N/T which is a pressure cast bit almost identical that Im sure it would work. Thats how different and how long it took Suzuki to deliver this stuff to the punters. By comparision to the TM400 clutch its like looking at a Belarus tractor next to a new John Deer.
