I have a 1986 KX80 and it is too much power for my son at this time. My thought is to swap in an engine that I have from a 1974-76 Honda XR75. At this point I don't have any money invested in the KX and XR parts. He is now riding a 1970 Honda trail 70, so the step up in size and suspension and overall handeling of the KX will be an improvement. Metal fabrication wont be my problem but I'm wondering about the location of the counter sproket when the engine is mounted. It looks like it will be farther forward and even possibly slightly lower than what it is now with the KX engine. The swing arm pivot bolt runs through the back of the KX engine and that wont be possible with the XR engine so it will have to move forward or down or both. Anybody got any ideas on this?