That leaves us with the disc valve cover. The little plastic gear (oil pump drive) in the centre of the crank unscrews by hand. Then it's time for the air gun to remove the crank nut and gear.
The disc cover is held by four screws, but take a little care when removing because they are always very tight. An impact screwdriver is probably the best way to remove these after so long.
One disc valve. The rusty stains actually wiped off with a rag and WD40! The crankcase surface the valve runs on is in excellent shape too. Just a little light pitting, and for Magnesium cases, that's pretty good.