10"drums front and 9"drums rear, what master Cylinder use?

I would try it just as it is, but would test the brakes hard to make sure the back stays in the back. But knowing those 9 inchers originally barely stopped skinny 13 inch tires, I don't see a problem. Pick someplace with lots of room, no traffic and some lightly sanded patches. Work up to skidding the front tires at something like 15 mph and see what happens, then a lil faster. If at any time the back skids first, you will need: a proportioning valve, or smaller rear wheel cylinders, or bigger front wheel cylinders,or bigger rear tires; whatever is easiest or cheapest. If the rear skids first, it will spin you out or could put you into a bad situation.