Since you've changed distributors & then added tune-up parts, it might not be the distributor. The GM HEI only needs 1 wire, a switched 12 hot to operate. I've seen situations where a malfunction in the keyswitch or starter soleniod can cut power to the HEI when cranking. Check to make sure the distributor is getting 12 volts in "start" and "run" positions of key. How many wires go from vehicle harness to distributor- One, two, four, etc? Regular HEI needs but 1 wire. The spark knock models used a bunch more wires between dizzy and truck harness. The ESC controlled dizzys didn't have built-in spark advance, it was done in the computer. And like other posters say, when they went bad, they went baaaaad.
You can check condition of timing chain with a compression tester. If you've got good compression, over 110 PSI, the timing chain and valvetrain is likely OK. Since rotor is spinning, a jumped chain wouldnt kill the spark. It might spit and pop, but not just "quit" and do nothing. I've seen chains jump and timing gears disintergrate from wear, a furd 302 and a chevy 307, and they'd both still kinda run, but badly. Changing the chain requires removal of crank pulley, water pump, timing cover, etc. Not a fun job.
