Hi Pete, your engine is an interesting one, so a few hassles are neither here nor there.
Your flywheel rotates clockwise, unless you have a really unusual mower. The firing mark has to reach the stationary mark before the TDC mark reaches the stationary mark - it fires 6 degrees before top dead center, not after TDC. To clarify this, just look at the flywheel and rotate it the way it normally rotates. To fire before TDC, the timing mark must get to the stationary mark before the TDC mark does. That means it has to be clockwise from the TDC mark, which means it is to the right of the TDC mark as you said. Do this a few times on the engine until you are convinced, or come back to me and tell me I'm full of prunes. Either way we'll work it out. Don't take my word for it, or you won't learn anything from this. Incidentally it is a tricky point, I always have to go through it carefully each time myself and I've been doing this a long time.
Try to get the timing mark as close as you can to the right place. You can probably manage to get it halfway between 8 and 9 mm, but 8 mm is pretty close. Whey you are really sure you are right, and have verified that is where it actually fires, try to make a nice pretty-looking permanent mark on the flywheel.
