as long as you can weld I say go for it
my boss has a 86 lt250 with a 89 750 ninja motor in it
I have a pic of it in my pics if your interested in seeing it
and if he can do it so can you

 

I did a conversion where I switched brands. If you have the wiring harness and all the electronics with the motor it helps alot. It took lots of fab/welding to do a 4 cylinder street bike engine. A single cylinder engine would be easier for sure