Randomly shuts off

"IF" it's ignition it's a crap shoot when heating.

Could be coil heating up and quitting.......used to be very VERY common

Could be the ECU

Could even be the dist.

Here's what I'd try. Try to get it to quit, but be prepared to do some testing so you can "jump out" and get right with it.

When it quits, leave the key "in run" and immediately check the coil plus and neg posts. You should have say, 6V or so on the pos, and very low on neg, 2V or less.

If the coil PLUS is high, the coil is not drawing current........bad ECU

If the coil NEG is also way higher than a couple volts, same thing as above.

If the coil POS is below 6V you may have a power problem. Check the ballast "key" side you should "same as battery."

Next, pull the distributor harness connector. Take up the engine side, and tap the bare end of the connector to ground. Should make a spark each time. No spark.....coil or ECU, assuming you have power at the ballast

If the above checks out, "try" a coil if you have a spare, and you should have, anyhow. Does not have to be the exact right coil.

This might also be the distributor pickup, but that would be rare.