If removing bottom hose doesn't work then try jacking the back of the car. Removing the heater feed bottom hose might help also by venting any lock since your car doesn't appear to have a heater flow control valve in keeping with the later 3.7.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone