I'm not sure why you would want to be 10 deg BTDC.
Here are the links to the pertinent parts of the GSM at Clarks:
http://www.clarks-garage.com/shop-manual/eng-06.htm
http://www.clarks-garage.com/shop-manual/eng-10.htm
You want to be at TDC on the crank
and on the camshaft. I've followed those directions and haven't had any problems yet.