All of the Chinese engines I have seen have been built with the mounting dimensions of the Honda 50-70 and TRX90, which is a smaller bolt pattern than ATC/CT/CL/S /SL 90's, and all the horizontal cylinder 110's and 125's. So they don't bolt right in, but can be adapted with a little plate steel for spacers and a couple of holes drilled. You will lose the cylinder head mount, and some say the frame is significantly weakened because of that. Your experience might be different, but if it were me, I'd source a running Honda engine or rebuilt what you have. Good luck!
1985 Tri-Z 250
1985 ATC250R