Hey Warden. Royal Purple is good stuff. I have it throughout a gasser that I'm selling right now.

When I changed my rear diff oil I went w/ 80w90 Redline sythetic. If memory serves me correctly I had two bottles. I had a little left over. When you are draining be sure to raise each end of the axle one end at a time to be sure to get as much of the old stuff out as possible.