Gear choice
That cam should easily let you do the 3.21 gear...but having gone through multiple gearsets here (over a number of years, but always behind a SB powered 727 drivetrain in the same car), I can say the following:
1) 2.94 - yikes...not good, for anything
2) 3.55 - what a 'day & night' difference that was, my ride was finally alive
3) 3.91 - aha, here we go: some business to do on the street
4) 4.10 - that's right, commit or go away (LOL)
These were all in the same chassis and tire sizes, 27.75" tall tire (275/65-15), I left out the converter and engine build details b/c I'm focusing on an overall assessment with the priority on the cruising 'feel'.
So yeah, that motor (408 W2 stroker) is pulling some RPMs at cruising speed (3700 @65), and with the header primary tubes sized at 1-7/8" and 3" X-pipe to the back, yup, she's a bit of a loud ride. But that is exactly what I wanted and besides, I only do about 3K miles a season on that thing.
Go 3.55s, I think you'll be happier!