Join Date: Jun 2011
Location: Colorado Springs
Dollars to doughnuts the PO removed the thermostat because it was overheating and he erroneiously thought this would help. You definitely need a thermostat in a 351 Cleveland; as mentioned, it's not like other Ford blocks. I would recommend going to NAPA to get it. Otherwise, the parts guy will try to sell you a Windsor thermostat and tell you all Ford V8 thermostats are the same.
Thus, since you'll be working on the cooling system anyway, it would be a good idea to pull the radiator and take it to a good shop. They will run a flow test on it and fix anything that needs fixing. Old Mustang radiators are notorious for getting clogged. And you cannot unclog it yourself.
Then, install the freshly cleaned radiator, new hoses, and the new thermostat. While you're at it, you might consider also replacing the water pump. Then you'll be golden!