The master cylinder on my 450 was the only part of the brake system I didnt replace when rebuilding the brake system. I gave the casting number to Geoff, he had it in stock. He also had all the wheel cylinders and a return spring kit for the front. He was a couple buck cheaper per item than locally. One word of caution, the return springs for the Eaton rear are unavailable. I had my hydrovac rebuilt locally a little cheaper than Geoff wanted for his, though he had one.
Scott