It's a piece of piss, PIN goes in hole uncovered by removal of 10mm bolt, to line crank up at TDC, them 8mm rod or flat bar in back of cams, the slot is OFFSET so will only go in the correct way.
The pin for the crank is a precise length so that a flat section on the web of the crank contacts the end of the pin so it can go no further and this is TDC.
tabetha