Help with Rear end gear ratio

I'd go 4.56 or 4.88's with a 30" tire. You're never going to hit 11's with a mild
318 but it will get you off the line. Besides , it will be the gear you'll want to use for you're future engine unless you build a stroker.
I used to have a link to a site called automath.com . It has a bunch of templates for calculating shift rpms, tire sizing etc....