I'm currently boilding an artcar out of two Suzuki bikes and came across the GS resource site. Someone did the research on quite a few lubricants. More than you ever wanted to know about oil.
Check out this link
http://www.gsresources.com/oil.html

Stefan Stout
80 450SEL
80 450SEL
80 280E
89 Jeep Commanche 4.0