RE"It would be great to see this same test done on a heathly 390 with stock heads. "

LOL Bob H after all the swapping, torquing, sore backs and scalded fingers those great guys had to endure not to mention Jays preference for big displacement and rather radical power I think you just might be better off clicking the heels of your Ruby Red Slippers Together and repeating:

I want a 390 Manifold Test
I want a 390 Manifold Test
I want a 390 Manifold Test

I'm just kidding but LOL