You can get aftermarket valves that are cable operated and just fit inline with one heater hose. You can also get a heater valve that screws in the water pump and the heater hose connects to it. Check NAPA.
Either will be relatively cheap, effective, and easy to install.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-