will 360 j heads fit on my 273

I've never understood why people think porting and polishing on a street head is a good idea. Going to a larger port will cause the velocities to drop quite a bit. Polishing will help with flow, but only in a motor capable of some deep breathing. Also, it can mess with the way the A/F mixture moves and atomizes through the port.

I could tell a story about the 346s I had on my Bee, but you would all think me nutz