Call Geoff at, Alretta Truck Parts. (508)788-9409. He just found another member here (appaloosas, on the 2nd page here) a master cyl. He'll know off the top of his head what you'll need. Knows these old truck brake parts, like the back of his hand.
Spanky Hardy Collector Of Fine Old G.M. COE Trucks & Antique Holmes Wreckers