Motor swap

[fzrr750]

Ok, guys, I have a question for you. Anybody know if I can swap an older air cooled motor (250) into my 89 KTM 250? I let my bike sit for about two years and the motor is froze up bad. I sold the radiator and stator to a buddy who was running his 88 KTM and since my KTM was sitting I thought I would make him happy. My 89 is in very good shape. Forks are tight and no leaks and the shock is great also. Bodywork is in very good shape and needs nothing (just a good cleaning from the last time I took it out in the rain (still has a little mud left on it). The frame is in great shape with a few small scrapes on it. I was going to part it out on Ebay this January, but keep changing my mind every time I go into my garage. It is sitting there next to my other vintage racers and I would like to keep it. Sine I do not race it, I do not care about the original motor being in there.
Any ideas, POG guys?  Thanks for your help.
Ed

71 Suzuki TM400,72 Suzuki TS400 Desert racer,76 Suzuki RM250,74 Yamaha MX360,79 KTM 250MX, 87 Yamaha FZRR750 X-endurance racer #112.