[Tom Kirkham]

I would encourage you to look at two upgrades:

Change the original 19 spline stub axles to the 30 spline stub axles.
Drill the holes for the diff cooler.
Drill a hole for a temp sensor.

For a street car I would look at using a Eaton TrueTrac diff unit. Very reliable, and almost maintenance free. Also available in 30 spline.

I have not had much luck with Auburn diff units.