A 1950 truck would have been manufactured with a "zero pressure" cooling system. Any radiator cap over about a 4 pound rating is going to put your heater core at risk. You're much more likely to put the engine at risk from a burst heater core than you will by letting the temp rise above 200 on occasion. Modern engines don't even turn an electric fan on below 220, so going a little above the theoretical boiling point with no pressure isn't as disastrous as some people think.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!