Yeah that's the trouble with 450's ...don't go round the corners too good.
Will you have to chop the frame up around the kickstart area or do they fit ok
The frame fits fine round the kick start. you have you cut the Y on the down tube and move it up for the exhaust port and cut and extend the bottom of the frame for the water pump. the size of a 500 engine is so much bigger than a 250 so its a pain to get in the frame
This is interesting stuff and seems to be a subject people have been playing with for years. My dad has a 1960 Greeves (alloy beam model) which started out as a 250cc 2 stroke. Someone later fitted a 500cc unit-construction Triumph motor in it (also from 1960) and ended up with a very light, very quick (for it's day) bike which looks a bit 'different' but handles surprisingly well. I'll see if I can find some photos to post.
The PBH in my album is dimensionally the same size as a 250 Honda - it uses the Honda plastics - but carries a 560cc Rotax fourstroke. Without doubt the best moto-crosser I ever had.