I did a butt load of these conversions, so many I hardly ever looked at the wiring diagram in the later years, but that was a long time ago.
Seems to me I pulled the IGN hot wire out of the Lean Burn harness (blue wire) and connected that to the IGN hot on the electronic conversion. I seldom did anything with the remaining Lean Burn harness except unplug it from the computer and tucked the end of it out of the way.
You will probably want a different air cleaner assembly as well, but the Lean Burn computer can be removed from the original air cleaner assembly, or the computer can just ride along. Gene