There are a couple of very informative threads on Discoweb.org, in the discovery technical section on the appropriate oil for these engines. Apparently the oil properties have changed since these trucks were originally manufactured. Do a search for either HTHS or oil, or the forum member name Chris St. Louis (real name Chris Schaeffer). He presented some really good technical information that was helpful. The point was, the 3.5, 3.9, 4.0 & 4.6 engines (all same basic design) were flat tappet engines and required an oil with a high temperature high sheer (HTHS) rating of 3.5 or higher. In those threads there are a list of oils that meet those specs and also instructions how to find that information on oil manufacturer data sheets (basically, go online and pull the data sheets off the respective product websites). Maybe that will help you in the future.
Received this in the mail today!
Plans are to install the cam, lifters, gear and chain, kick down cable, LED rock lights, new canvas slings for both front seats starting next Wednesday. I plan on taking a lot of pictures and reporting in every evening.