When using the rear wheel with top gear engaged, I was told to bump the engine forward slightly past your chosen full advance position, then bump backwards towards your desired setting, to put the lash in the state it would be when the engine is pushing the drive train, then tighten up the ATD on the magneto taper. Is that correct?
Sorry Steve, that is not the way. You are quite right to worry about backlash but the backlash that we are interested in is that between the crankshaft and the magneto. For that reason you turn the crank forwards up to your timing point. The method of turning the crank is unimportant so backlash in the primary/gearbox being in the wrong direction doesn't matter.
I seem to spend most of my life shouting at apprentices "Don't turn the ####### thing backwards " when setting timing.
Cheers
Peter