I know that you don't need a lot of spring pressure to make these things rev. I tried building this engine with eagle heads and a carb at first, but I was using the same theory as a small block when setting up the springs. I was setting them up with close to 700 lbs of open pressure-- needless to say I was breaking rocker arms like twigs. After breaking the rocker stands on one of the heads I took my 6.1 heads to Barton. My jaw hit the floor when he told me they were twisting them to 8000 with around 400 pounds of open pressure. I would say if you went with the Manley springs- you should be safe twisting it a little higher. Keep in mind that you want to keep everything as light as possible ( titanium retainers & keepers).
