My question can you put a buell motor in a paughco rigid frame and use the same motor mounts as a sportster?

Depends on the year buell.

the what year buell could i use on a sporster(evo) rigid frame?

The frame should be year specific and have specs as to which engines will mount direct to it. If not, do you know a good welder?

I think most of the early or "Tubers" as they are called will fit the 86-03 type frames but william is correct there should be specs on the frame as to which 1 would fit. I am using an 98 m2 cyclone for a build and the frame i'm getting will take any sportster engine 86-03 or tube frame buell engine.