If you want 6 lug, get one from a '73-'76 GM 1/2 ton 4x4. For 5 lug, depends on which size 5 lug you want. If you go with the Truck 12 bolt, it will have a 5x5 bolt pattern. The Passenger 12 bolt (common in full size cars and big block powered Camaro and Chevelle) wil have the 5x4.75 bolt pattern. The latter will be a bit easier to find wheels for.
The stock rear is well up for task (I've seen them handle well over 1000 horses), but is limited in gear ratios and the Posi for it is very rare.
