kill switch

You need to disable something that thieves are not likely to see, realize, or be able to figure on quickly. Disabling the starter cranking circuit is a waste of time, because any good thief can just jumper the starter solenoid.

This is why killing the fuel pump relay is good, and might even be a good reason to switch to an electric pump.

Grounding the coil NEG is OK if you do NOT have MSD, and with MSD grounding the white "Might" be OK, ..............GEE ............ I wonder how many thieves "have" "the internet" and might be really ready for THAT??

I'm not sure how else you could disable an MSD

That's why I suggested a fuel selector valve. You CAN buy electric shutoff valves, as well

This is a Standard. Pollak and others make them, not that expensive