From what I can tell, all of the '79-82 heads will bolt onto the FT engine, but the FT exhaust will not bolt up to the XL/XR heads; the ends of the FT pipes and copper o-rings are much larger than the XL/XR. Also, on the intake side there may be issues, depending on the year. I know the '82 XR has a very different intake port than the FT, and the FT carb won't bolt right on.