Michael and Rick make interesting suggestions. I now remember a problem back in the '70s. A friend had a similar issue with his Spitfire. He had changed the plugs and other ignition parts, but had not checked that the plugs were the correct heat range- or at least the same type that he had been using. The car dieseled badly, and he chased the problem for a couple of weekends, unfortunately messing up almost everything that he could adjust. An "old guy" (probably about 31) that we knew figured out the new plugs were two steps hotter. Replacing them with the original parts solved the problem.
Were your plugs changed?
As to the electronic ignition, I assume (and that can be bad!) that by replacing the points with the pick-up hardware for the electronic ignition, the timing could have advanced (like adjusting the points affects the timing). That could cause the car to run on. Jim