Use the safety chain and chicken hose method, and hide behind something sturdy before attempting to raise the pressure. You have no idea what condition those locking lips are in. The rule of thumb we always used for adding pressure to an inflated tire was NOT to do it if the pressure was 10% or more low (8 PSI on those 80 pound tires). The safe way would be to deflate, disassemble, clean and inspect the mating surfaces, and then decide whether or not to re-inflate or scrap the rims. The tricky part would be finding a tire shop willing to do that if you don't have the tools and/or experience to do it yourself.
The force exerted by the sidewalls on that locking lip is measured in the tens of TONS- - - -the name "widowmaker" was not conferred lightly on that design of wheel.
Jerry
