If you don't plan to tow anything 3.08 should be economical. I had a 59 gmc 1/2 ton with that ratio, and it got around town just fine. I kept up with traffic on the freeway at 80mph too. Oh yeah, it had a 6 banger in it, your 350 should move just fine.
If you want better acceleration you could try 3.55, 3.73, 3.90, or even 4.11. By lowering the gears you will sacrifice both top end speed, and economy. If you are running a 700R4 you can go with lower gears. If you are using a TH350 or 400, 3.55 gears would probably be the best city/ highway gears
A 10 bolt seems a little small for your application. Chevy 10 and 12 bolts are not particularly strong axles. They use a c clip design that wears as you drive it. If you were going to spend money on that axle to change the gears, I would look into a stronger axle such as a dana 44, dana 60, or Ferd 9 inch. The 9 inch is the strongest and cheapest to get parts for. The 9 is also the easiest to work on. I have heard that you can swap out the gears in a ferd axle in your driveway in about an hour. You could have 1 ratio eg 4.11 for racing or towing, and another for highway economy.
Check out
www.4lo.com it is a 4wd sight that has gear calculators. You can fill in your numbers to see how the gears affect rpms, or speed. Fill in 1 for transfercase ratio, and 1 for transmission ratio... unless you have overdrive.
The Nova axle is not a bad axle for your application. There are better axles available. It all depends on the time and money. Crunch the numbers and ask a lot of questions. Axle swaps can be costly, and you only want to do it once.
