And "maybe" adjust the power valve. I think the rule of thumb is to run a power valve that is half your idle vacuum....so you need 13" Hg vacuum. And yes, the 6.5 is stock.
There are two (at least!) competing theory as to power valve sizing. If you want to experiment, I suggest BIG swings to determine which direction works, for YOU. Highest available, (ten something, I don't know exactly) and a 3.5.
(A lot easier to test on a four barrel than a sixpack.)