First the Oval port head does not have enough runner volume to support 496 CID at 6500 rpm. To do so you are going to need a square port in the 320 CC range. With the heads you have and that CID your looking at about 5200. I would suggest going with an air gap intake.
Larger valves will help but then due to the runner volume you are limited. I would put a set of 2.19 and 1.88 in the head. This will help move air in the mid lift numbers.