Finally got off my arse - overcame my fears, of reassembling my SL350 engine, never done a twin before. installed the new .50 over pistons and rings, and slide on the jugs, whew! , then the head, pulled the cam chain up through and installed the cam with the L mark facing left and line horizontal with dowel pin on end of cam facing up. I also ensure the left piston was at TDC and the crank wood ruff key was facing up. I think I am on track! Maybe these old twins are not that hard after all.