Suzuki RM125 1977

Are they the same cases?
The cylinder and crank have a different bore and stroke
Sounds like more trouble than its worth.

Just find a complete 78 engine and rebuild it. Most engine parts are still available NOS. The 78 was well evolved and runs better than its' predecessors.

Yes you will need a '77/'78 crank, cyl and head. '77/'78 parts are much easier to find too!

If you go this route I'd be interested in your '76 parts? Do you know what bore the Cyl is at?

You will need 1976 parts. Sell what you have to Minifig-Phil and you can find a motor on ebay or Mark's swapmeet. I suggest you find 1977 cases in the event you want to race an AHRMA event one day. All the 1978 internals will fit in but you need the 1977 serial number on it! Otherwise the 1978 swaps completely in as mentioned above.

I have a few 77 RM 125 motors, frames, forks, tanks, seats etc...if interested , shoot me a PM...