The larger sized piston is a PILOT number 10534 and the smaller is 12406, but the interchange book (Pilot PH 16-B, dated 1/1/69 revision) shows the size as only 13/16th inch. The same book says the Wheel Cylinder as a complete assembly is same as used on 1950-55 Nash Rambler and 1953-54 HJ. The Front wheel cylinders interchange with L & R 1953-54 Hudson according to the book. This may help track parts down.