Originally Posted by GSD4ME
Looks like it started life as a 19 litre off a twin shock R65, or R80ST.
Well, unless you're talking about an R65G/S which is pretty rare. Otherwise it's prolly R80G/S. The R65 (non G/S) is reeeaaal similar, but doesn't have the extra swoop at the knee. Plus, I doubt the R65's ever had a vented screw on cap option (only avail in the first year or two of G/S series).