Easy answer is with the key. The DeSoto sounds like a very cool find.
The stuff that I hear the old timers swear by is putting a little Marvel Mystery Oil in the top of the cylinders and let set overnight. After replacing the fluids, even turning the engine over by hand will prime the oil pump and push the new oil through the engine. With a good oil pump, 3-5 revolutions has established flow.
If the carb is streaming fuel, then I'd rebuild. It may seep a while as the seals are swelling up from gas. IMHO.