the cyl bore dim's might be the same
But the cylinder FINS on the PA's are definately larger than the others
(which is better in generalb - for cooling)
... ha ... but now I can't remeber if the mounting stud loc is the same or not
It would be great if all the top end parts were swappable ... pick the best head ... best cyl ... best carb ... best piston ... etc etc
just small improvements in all those areas individually ... and you'd have a pretty quick bike ... from all stock parts