Some may use an oil additive to compensate for the specific product they are using in an application. Others will recommend that premium products be used instead. This would include:
Engine: Premium grade FULL synthetic engine oil - 20W50 (this would excluded SYN3)
Tranny: Premium grade FULL synthetic GEAR lube - 75W90 or 75W140. GL-1 or better in 5-spds, GL-5 in 6-spds
Primary: Premium grade "fit-for-purpose" oil like HD Formula + or Spectro Primary. Ensure NO friction modifiers in your choice here.
In my twin cam 88 I run Amsoil in the engine, transmission, and primary. Somewhere on this forum there is a survey of what oils peoplel are running. Amsoil was rated pretty high so I tried it, liked it, and stayed with it.