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After rewiring My 1952 M38A1 with a new electrical harness, and having the engine rebuilt all seems well. Two lingering issues I have had and wonder if others have answers for.
Leaving my Jeep sit for a few days, it seems I have a Battery drain in the system even if the switch on the dash is off, leading to maybe one try to get the motor started before the battery loses cranking amps. Then I have to recharge the battery. I thought for a moment about putting in a cut-off switch on the battery but the market ones seem to big for the battery box. Is putting a switch on the ground wire an option under the hood?
Between that and the gas locking up after running for 30mins I think I need to put in a gas stop cock to keep gas in the lines? Should that be closer to the engine versus just inside where the fuel line comes into engine compartment?

Most common leak point is the starter solenoid/switch. Carbon and copper collect on the contact plates for years until it allows the juice to drain to an internal ground created by the metallic dust. Usually opening up the switch and cleaning contacts solves the issue. If by some odd curse the leak is somewhere else then remove the battery plus cable going to the starter and connect a 12V or 24V test lamp to it. If the lamp glows you have a leak. Now disconnect one circuit at a time until the lamp goes out. 2nd most common leak source is the light switch. You can also make this test with a VOM placed in series instead of the test lamp. Just study your wiring diagram and figure out which lead or which fuse isolates which circuit. As to your original question, yes you can attach the battery open switch to the ground or the positive posts. There are also several variants of those switches including blade types.