That's the point I'm at. These have a .96 a/r on the exhaust, I believe he makes a .84 ar housing, I wonder if that would be worth a shot? When I purchased them he had said they work great on 5.3 and 6 l ls engines, but after talking to some friends they said you really can't compare an ls to a sbc in terms of flow, which I really never thought about.Only thing left is the turbos. Will Viren test them for you?
I know a lot of people have good luck with the Ching Chong turbos but I would try the Borg s366 and not look back. If everything else checks out what else could it be?