I don't know about phiilp's '38 VB, but my '35 VB is NOT pressurized at all. The 2000' climb from town to home (3000') over about 6 miles works the cooling system pretty well. Right now in the summer, the large and easily read gauge won't go over 165 during that climb. While 180 isn't dangerously hot, it is indicative of a problem. I totally disagree that an engine connected to a properly functioning cooling system will runs at what temp it wants. The only reason to have a thermostat is to have the engine run where you want it to.
A couple of questions; does your truck have a heater? If not, how is the heater supply/return plumbed? Some folks will simply put a piece of hose from supply to return. This allows some coolant to bypass the radiator, and that doesn't help. That circuit should be blocked off, not free flowing if you have no heater. Having a heater core in that circuit actually provides more cooling in operation, and doesn't subtract from cooling efficiency when it's not. That's not true of a straight piece of hose.
Are you running an antifreeze mixture or straight water? While antifreeze wasn't in common use until after WWII, is really is a good thing to use, as it does allow for better cooling and inhibit corrosion. If you run antifreeze, be mindful of overflow, it's sweet taste will have animals ingesting it, and it is poison to them. You can put an overflow catch bag on an unpressurized system, but you have to mount it on the firewall at the same height as the radiator coolant level if you do.
Running with no thermostat BTW, CAN make an engine run hotter. The coolant can spend so little time in the radiator that insufficient heat is transferred, resulting in a loss of efficiency.
