Does your radiator neck have provision for a pressure cap ? I believe the overflow tube needs to come off the neck at the cap so coolant will only come out when the cap lifts.
I'm putting a new 235 into my '40 and have been thinking about the same issue. My radiator has a 0 pound cap and the overflow tube comes off the top of the radiator, not the filler neck. I expect to have to have the neck changed to take a pressure cap and move the overflow tube to the neck.
Steve
