New motor for 81 XJ 550?

I've been thinking about parting out my 81 XJ 550 as I've worked on the motor and have also had it professionally looked at and still cant get it running properly. I've read all the info I can get my hands on from the forums, done all of the troubleshooting reccommended and even ordered parts from Chacal. So I've come to the solution I'm just going to make it into a custom bike and would like to replace the motor and would like to know who sells new motors that would fit the 550 frame, with little to no modification, or how would I find out what would fit? Thanks in advance!!

 

'Tain't no such thing. Anything other than another 550 motor isn't going to fit your frame (ok, maybe an FJ600 or Radian 600 motor.) It's not a Harley, you can't just go out and buy a "new" motor.

Used motor with fewer miles, sure. eBay, scrapyards, donor bike off CL-- lots of ways to find another motor.

What's so horribly wrong with your 550 that no one can fix?

Which 550 is it, how many miles are on it, how long have you had it, what have you done so far? Where are you located? (Most of these answers belong in your signature and profile, BTW.)