Unfortunately at my age what I THINK I remember sometimes contradicts what is correct.  So I've got a '72 RT1MX engine on the shelf and somebody let the chain get loose and bust the left case.  Based on swapping some GYT Kit stuff around on my old '71 DT1 enduro back in the day I'm pretty sure I remember that the 250 and 360 jugs had a difference in the bottom and would not interchange.  Online parts breakdowns seem to support this with different part numbers for the base gaskets, at least for '71.  When I do the same search for a '72 it looks as though the left case carries the same part number on both 250 and 360 AND somebody has a left case on E Bay now with a listing that it fits both DT1 and RT1 even though it has a DT serial number.  

So the question is, exactly what cases will interchange to the '72 RT2MX, or more specifically was there a change in '72 where the same cases could accomodate both cylinders?

And one other question while I'm at it.  I'm also of the opinion that the late style cases like came around on the '74 250 and 360 WILL NOT bolt to the earlier frame, so this '72 360MX egine I have won't bolt in my friend's '74 360 enduro frame................... correct????

You're smart to ask... 

Dozens and dozens of posts on the importance of the part number prefix (model code) and how the new electronic parts lists cause confusion...  Original parts lists were shared by similar models (250 and 360 for example) and often had specific model identification information that was lost in the transition to the online parts lists. 

And to add to the confusion, sometimes the model code prefix you need for the part you want is not the obvious one.  Luckily that's rare.

The above (mostly the shared lists) is why there are so many "magic" parts on Ebay...  pistons that fit both a 250 and 360 for example. 

So no, you can't use a 250 case on a 360. 

(But the 125/175 shared the same crank dimensions so you can swap cases among similar 125/175 models.)

I don't know for sure about the mounts on the 250/360...  I do know the 74 DT250/360 models were based on the major engine and frame redesign of the 73 250/360/500 MX models so my guess is a pre-74 enduro 360 engine won't bolt right into a 74 DT360...  but the 73 MX250/360/500 might fit.

One of the experts will probably be along with a definitive answer on what swaps into what.


 

Thanks