Over Voltage with New Battery Disconnect Switch

Just looked at your switch. You could get a second and make a mechanical linkage that would shut off both at the same time.

I would also look into what 67dart273 pointed out about voltage drop etc.

Lastly... 60s ford starter relays are cheap and beefy. Could use them to do the disconnecting and use your switch to do the controling. Dont know if it would qualify for NHRA????