/6 runs great, randomly stumbles and dies...???

Could be many things. Indeed, everything needs to be almost perfect for an engine to run smoothly. You need more diagnostics. To rule out spark, get an in-line spark tester (cheap @ Harbor Freight). Stop and install it when it starts acting up. Maybe easier for catching it in the act, is to run 2 wires from coil+ and BATT- into the cabin and monitor with a multimeter (cheap/free @ HF). If you see it drop <8 V, investigate further. Carry a can of starter fluid and spray it down the carb throat when it is running bad and see if that smooths it. If so, you are running lean. Once the engine warms up, the choke plate should be strongly open.

My 1st suspicion would be a wiring problem, like a poor ground on the ignition module. You wouldn't see that from the coil+ reading. Who converted it to electronic ign? I have seen a lot of Billy-Bob jobs, like wrapped wires w/ scotch tape. For some reason, many think electrical stuff is magic, so doesn't matter if they half-@ss it, as long as they pray to the gods. Post photos.