What's interesting about the 337 is the as-cast head flange ports are small for a true MW, I think they did that in case somebody wanted to use it on a well relieved standard port.

The other thing is that with the ports opened up to ~1.3" x 2.6" the plenum to runner transition port opening is Huge by comparison, Mine is ported to almost the size of a business card in square area. That's a good amount of port taper across maybe only 5.75" of runner length. It would be a torque killer on 440 cubes but I'm hoping with a 4.300" stroke 517 with 11.7:1 CR it will pull very well.