His power is not that low. 340-350 should be pretty spot on for that combo.
I made 385/415 with a KB at 8# with a 255 pump 38# inj. My issue was a pegged MAF from going any higher. That was Stock SB AFR 165's Crower 15511 and Ported GT40 with the KB2200 Blowzilla.
I was hoping to break 400...