Quick update with some harder numbers on a 496 I put together last year. It's B wedge based (383 so 4.28x4.25 but with a shorter rod than the RB 4.15/7.1" rod), 10.7:1, ported Shady Dell Stealth heads, RPM intake, Comp solid flat tappet by Dwayne Porter, Porter Racing Heads with .499/.515 after lash, mid 240s duration at .050. It was designed to be run on factory exh manifolds & exhaust and actually won at Carlise in Stock E body. In that configuration it made 448/458 to the tires on pump 91. The owner recently replaced the smaller carb with a 950, and manifolds/pipes with headers and 3" pipes. It made 480hp/482tq to the tires this afternoon on the same dyno. It pulls 15" of vacuum idling at 800rpm and runs the power brakes too. The secret is to match the entire package. I think your (OP) static ratio is a little high so you'll have to go bigger. If the block has already been machined (meaning for me it's too late for lifter bore bushings) I would go solid flat tappet. Duration of at least 250. Lunati's got a Drag Race solid grind that looks good - 30210917. Comp's Magnum 21-249-4 or Drag Race XTQ294S-8 would be good choices. I think of all of them the XTQ294S would be my top choice.