Here's a response I got from a quick Google search about Redline Shockproof in transmissions. I asked HD about using full syn 20-50 engine oil in all three holes, and that is what they recommend. I thought about using the Redline, but I think I'll continue to shop around.
"REDLINE SHOCKPROOF There are concerns about using REDLINE SHOCKPROOF type gear oils inside manual transmissions. While this is truly an excellent product, it has been found that the heavy Teflon-like particles are quickly centrifuged out of the oil and will build up inside the center diff housing and around the synchronizers and inside of the gearshafts. After several oil changes this build up may block oiling passages inside the gearshafts that lubricate the needle bearings and can reduce the overall effectiveness of the synchronizers, leading to poor shift quality. Also this oil is has too high of a viscosity for winter use. Therefore we do not suggest using SHOCKPROOF in the transmission unless the transmission is to be serviced often or a dog box."