Welcome!
You've hit some hot buttons for me. I had an '88 CR125 that I was going to do the same thing with, but a buddy of mine needed it more, so I gave it to him. He bought a Gio dirt bike with a CG230, and we intend to transplant it into his CR. He's around 6'3", so the CR will suit him much better than the Gio (which is a small wheel bike).
Did you have to get creative with lower motor mounts, or could you use the CR mounts on the XR engine? I spotted that you'll need to do something custom on the upper mount. I'll be watching for your solution, and then I'll promptly steal it.
Fundamentally, your new cylinder isn't actually a 250 kit, in the same way an SR250 Yamaha is actually around 230. There isn't a 250 combo for a CG motor that I'm aware of, unless you want to go liquid cooled. The three-wheeled trucks from China often use that setup, which gets near 270cc, IIRC.
Is the wristpin diameter the same on your new cylinder as on the XR200? Is it the same as your China motor?