351C and MSD ignition problem

Does your car have a factory tachometer? Did your set up come with an instruction sheet? Not to sound snarky, but there are a few choices on how to wire the car, on the instructions. Check the MSD website, they should be available there to look at...

It really sounds like you wired it wrong to me. The distributor would not be able to make a ground source (-) read 12v. If there is ground on one end of the wire the whole wire will read near as makes no difference to 0 volts. I think you must have wired a 12v source to the distributor ground.

dfayette,
The fact that you say:
"Engine cranks well and fires right up. I release the starter and the motor dies."
tells us that the distributor and MSD box (if its hooked up) must be working, but you likely have the "power on" feed hooked up incorrectly. On the original wiring, the wire to the coil is fed from 2 different places:
1>From the "run" terminal of the ignition switch, through a resistor wire, giving you 6-ish volts at the coil during normal running/operation.
2>From the small terminal on the starter wire side of the solenoid, giving you a full 12 volts at the coil "ONLY" when the starter is engaged.
These 2 feeds "Y" together somewhere in the harness. It sounds as if you are only hooked up to the feed coming from the solenoid, thus your issue
HTH,
Gene.

Cool, thanks for posting the fix! Most of the time these threads go open ended..