I wonder what the chances are for retrofitting the 360 cylinder on the old 300? Is the 360 watercooled?

 

The 360 is air cooled. I don't know if anyone makes a big bore kit for the 300, but if they do it would be cheaper. Not only cheaper, but the 360 top end probaly would not fit due to the bore in the case of the 300 not matching the bore in the 360. Good luck no matter what trail you travel.