Hi Rob and Dad,
"How do you add a 30 deg mark to the flywheel?"
Well, you already have Top Dead Centre and 6 degrees before TDC, so you know the spacing for 6 degrees. Using that spacing you continue round the flywheel. You're going to be looking for 30 degrees more than the previous mark, so five more spacings will give you the final 36 before TDC mark.
Tippex in the 36 and maybe the 24 degrees, and any others you fancy while you are at it.
I previously tried an adjustable timing light and found it extremely fiddly.
Hope it runs well afterwards!
h8v