yes this also can be done
ive got an article on this. its pretty straight forward too. The RM or PE 250 motor can go in a 175 PE floater frame. ive thought of doing this but im not sure about how the PE 175 frame would take the extra weight and power of the 250 and if it would be too squirelly??? maybe a better option to fit a 250 PE motor to a air cooled fullfoater RM 250/465 frame (seen this before too)
when i get this article on the 250 pipe fitted to 175 i will tell you about it.
im sort of with cyclegod here, im not sure why many people try to build serious power MX bikes out of a PE? fair enough if you just wanna strip it down and fit MX fenders, but when your getting to the point of trying to make it exactly like a RM, wouldnt you be better off with a RM in the first place?
is it because PE's are generally cheaper and more common and RM's are too hard to find?