I think the intake manifold may be a limiting factor. I have used in a couple of different street engines and managed to make over 600 hp with both (in the end), on pump gas. Had to play with the camshaft a little with the first one to get there, .54" lift, but the other one did it with off the shelf comp street roller, with .59" lift. Still I feel, they would have produced better power with a single plane, and the low end wasn't that great eirher.