Thanks all for the support. Maybe the following will help someone else. I was able to cobble together a decent test system. I found an expandable plug at Ace for the top opening of the radiator. I found a bourdon tube dial type tire pressure gauge at Ace that read clearly in the range of 0 to 10 (and beyond) AND would allow me to unscrew the external piece that fit on to the tire Schrader valve. A few brass bits adapted it to a 1/4" barbed nipple. Amazon had a Schrader valve that terminated in a threaded fitting. I did have to turn down the tip of the valve slightly to get my air chuck onto it - my compressor does adjust to very low pressure, no damage to any cores. Some fuel line allowed me to couple this into the radiator overflow port. The results were good.
Bob
