Here is a posted description of how to set the belt timing:
http://en.allexperts.com/q/Small-Engines-Lawn-1746/2009/2/set-timing-GCV-160.htmThe GSV190A manual says "Set the piston at top dead center of the compression stroke (both valves fully closed). Top dead center of the compression stroke is in the position where the cylinder head cover mating surface is in line with the cam pulley alignment marks." This seems to be the same thing the website says. Two references that agree, and one of them is the designer of the engine, sounds like pretty good evidence that is how you verify or set the timing. Furthermore, that sounds fairly much like what you intended to do anyway, but it is the top of the cylinder head, not the block.
Please let us know what you find when you make that check.
