building 8 3/4 489 section

I think he's just talking about building another center section, not a whole new axle.

For a car that's only going 12's, all those billet parts are probably way overkill. I would still consider running a spool on the street if your tires are tall. (28"+) The best way to pick gears is to use a calculator to help you figure out what your theoretical top speed in 4th (or 3rd on an auto, whatever 1:1 is) will be. Ringpinion.com has some helpful pages for that. Figure out what mph you will eventually want to trap in the 1/4 and gear the car so you'll be right around redline at the stripe.