5.2/5.9 H.P build guesstimate

I second what @rumblefish360 says.

If you can spring for the 5.9 you should.

The 5.9 will make more torque/power at every point on the curve.

Carefully consider cam spec with the converter and gears you're planning on running. Aftermarket cams paired with highway gears and low stall converters is a recipe for a dog.