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

sounds like somebody swapped the whole rear axle assembly and just kept the 9 inch brake stuff that was on it (6 cylinder car). I presume that it has a 7 1/4 inch rear? If so I can ship you the whole 10 inch brake assembly to match your front brakes off a 7 1/4 inch rear end that I pulled from my 70 Dart (going to a 8 3/4 rear axle). I'd do it for $50 plus the shipping. If you are interested PM me.

Chrysler certainly never sold a car with mismatched brakes like that and for good reason...