First off, those heads are TOO FING SMALL for 400 inches. Anyone that thinks they are too big has spent too much time burning the hippie lettuce.
Second, as I say all the time, you can't go by flow numbers. That engine would be 70-80 HP better with a set of W2 heads with nothing but a quality valve job.
The intake manifold was wrong. So was using EFI like that on that intake.
Again, if Grey says that's what it makes, I believe him.
But to say those heads are too big is *** backwards and full blown retarded.