How do you plan to warm up the engine if it doesn’t start? Propane or acetylene??

By “pressure tester” do you mean compression gauge? Because that won’t work for leak down testing. Compression gauges retain the reading because of the valve stem, but the pressure inside the chamber quickly leaks out anywhere it can - even if there’s no other leaks, it will get past the rings.

With leak down testing, there’s a constant air supply into the chamber from the gauge via the spark plug hole. The gauge reads out the percentage of leaking present with ranges for normal, moderate, and high leaking. If it’s above the normal range, you can listen for air from the crankcase, intake, exhaust, or look for bubbles in the radiator to determine what the cause of the leak might be.

This can be done without the engine being warm, and I suggest doing it now because you’re only a few steps away from pulling the head IF a leak down test indicates it’s necessary. Even cold, a properly sealed combustion chamber should be within the normal range, or maybe just outside of it. The results are not “black and white” but need to be interpreted accordingly, as with any diagnostic test.