390 w/open chamber heads

Here are some heads. One is a 318 the other 360 (596 casting). I put the intake metal gasket on each and of course there is a big difference. When I installed the Performer intake on my Cuda I blended the ports with 302 casting (318) heads. I remember only having to do a little blending. As you can see the 360 head on the top of the pic has much taller ports and also a little wider. That's why so many people say to use the RPM. I don't have an RPM so I'd have to check one against the 360 head to complete my analysis. If the RPM ports are bigger and closer to the 360 ports then it would probably flow much better. NOW...I'm not saying the Performer won't work. I'm just saying that the RPM (if it has larger ports) SHOULD flow a lot better and smother with less loss of pressure as the gases transition from the intake to the head.
Fluid dynamics dictate flow and pressure when transitioning from one diameter to another. When a gas moves from one volume and pressure to a larger volume there's always a pressure drop (just like the air coming out of an air hose). High pressure in the hose then much lower pressure as it is released into the atmosphere. I may be over thinking it but it's still a fact.
Whether or not it makes a big difference...that's another question. But one thing is for sure. I can start with the Performer and always switch later, maybe I'll run across a good deal (RPM) between now and then.
DOES ANYONE HAVE OE THEY CAN CHECK FOR PORT SIZE????
Second pic is 318, lots of material to remove. 3rd pic is 360 head, much less material to remove.

Like I said I'll probably square the block if it's more than .003 out of square.

Treblig in Tex