It probably won't be a direct swap with an XL 100, they (if I remember correctly) are based on the XR 75 motor. The only 100 frames that a XR200/Chinese motor/CRF 230 etc. will fit are the SL/CL/CB100 from the early 70s, but even then, you'd have to remake the top mount because they have a taller deck height, I think the XR185 started the third revision of this motor with a 12mm taller head mount, though I think they might have changed when they went from the one piece head to the two piece starting with the release of the first TL 125 model. If you need more details, feel free to send me a PM. Sorry for polluting the thread!