I have built many of these rear ends with the 30 splin Eaton Posi and 30 spline Moser axles. I use Yukon gears and installation kits. This will give you a good strong rear end that's ready for future power upgrades. One suggestion that I have with the 8.5 rear ends is to weld the axle tubes. The plug welds on these rear ends are not very good and they have been known to break loose and let the rear end twist up. Welding the tubes is not a simple job. It requires nickel rods or wire and skill for welding steel to cast iron, but it's worth it. You don't want the drive shaft and pinion yoke sticking up through the floor under the rear seat. If it will never have slicks on it and if you have wheel hop completely under controll then you can probably skip this. Read this before trying to weld the tubes.
This is one that I did with nickel wire.