Just as an FYI, pulling off a battery terminal when the alternator is running can damage/kill the alternator or regulator.
How long sitting does it take to kill the battery? If this is a race car, why do you not have a battery cutoff switch? Most/many sanctioning organizations require them....or is that what you are calling a 'power switch'?
Waht HEI do you have?? We do not know if the HEI circuitry is wired correctly. Maybe he just needs a good wiring diagram for whatever ignition system he has.