motor swap on a CR 125

[Bikeopheliac]

Ive got a few motors laying around (85,88,90,00 CR 125). Im wondering if my 88 or 90 motors, which both have new cranks, would work in my 2000 frame. My 2000 motor still needs a cylinder and powervalve so Id rather use one of my rebuilt, complete motors I have. The crankcase covers are identical, and I compared my left crankcase half of the 90 with the 00 and everything lined up. So Im pretty positive it will work, and Ill just use all the old electrics w/ the old motor.
So, my question is will I have to go with a 2000 pipe/silencer so it will fit my frame or can I use the old one for now. Any does anyone know of any other things that might make this swap difficult?

 

[Chokey]

The carb, air boot, and exhaust will certainly be different. I don't know about the engine mounts or the head stay. Stick it in the frame and see how everything lines up...you already have all of the parts, all it will take to learn if this is feasable is a little time.