Tuning Street Demon carb

Hysteric,
He is not pushing any 'limits' here. His Mallory box could be faulty, but it has sufficient operating voltage.
CD ign has MUCH greater energy content than inductive ign.
O2 sensors need a power supply, which if it was low by 0.5 volt could be why your reading changed...or maybe it was just faulty.
The engine cranks & starts, an indication that there is more than sufficient ign voltage because voltage drops during cranking from the load of the starter.

I have installed two SD carbs. One, a 625 worked flawlessly. The other a 750 always had a flat spot. In desperation, the owner rang Holley [ from here ] but were unable to help. The problem was fixed by re-fitting the original QJ carb. Ign was HEI, which was not touched.