I would have to agree with the above reply, you need more air to feed that 496 than those closed chambered peanut port heads can deliver, those heads are more suited to smaller CI motors like a 396 or 427. Not saying they wouldn't work but it would be like trying to cram a gallon of gas thru a straw.
Invested in some good retangular port heads with open chambers.
Goodluck, Charles