They make thermostats that fail in the open rather than the closed position. Take the thermostat to a good parts house or garage and discuss this concept with them. This change is probably saving a lot of engines today.
Look hard for a booster pump, that seems like a long run thru a hose with the standard engine water pump to overcome. Keep at it, don't loose that engine.
Check all the hoses, when they get soft the tend to suck shut.