Zippy... Thanks for a very informative post!

To the OP, I am using the Professional Products Airgap RPM knockoff in my build and was told by someone knowledgeable on the magnum engines that it should produce more HP than the Mopar M1 single plane intake. They stated that the M1 wasn't a great intake.

If my Flamethrower distributor would hurry up and get here I would fire mine up and have some real feedback on the combo. It does make me feel confident that my 400-425 HP goal is attainable since the same cam was/is used on the 380, 390, and 435 horse crate engines. I know it's all in the heads, but I hope to see the high side of 400 with my slightly cleaned up plain magnums. Maybe I' m too optimistic...