Not without serious modifications to the frame and gas tank. Lower spars and down tube.
The 450 Frames are built around the motor and suspension for that power and torque. Conversely the same with the 250. Not saying it can not be done. If you have the time and the ability.
Note. The 02-04 450 motor mounts are the common I believe. 05-06 common,
07 different 08 different yet.
Try ebay or you could try Service Honda or any of those shops that make hybrid 500's.
Do you every share your access to salvaged bikes? Looking for some extra wheels and misc. parts.