"cr500" in a "cr250 1997-02"

I'm looking into a cr500, to later use the motor in an cr250 or crf450 [the crf first year is 2002, & chasis might fit the motor with less work]. Want to know if; #1 Do cr500 1988-01 motors all have the same motormount styles. #2 Do all the central aluminum frames cr250 1997-02 have the same size engine compartment. I was already told they bolt on frame in rear the same. Only front needs more room & other minor: tank, shimms, etc.. Don't want to mess to much with front frame welding "their might be no other way around it. crf450's are to expensive for a project!
If anyone has some Info please SEND IT BRO!!!!!!