I am talking about the one in the photo which is the Lambada harness!

Re-awakening this thread as I am doing this exact conversion - installing a 1980 3.0L into a 1976 chassis. Running carbs so might be a bit easier. Terminals #7 and #8 on the 14 pin connector on the 76 911 side I can't seem to find on the wiring diagrams. They terminate on "heater/blower" for #7 and "T1g" for #8. no clear routing shown on Porsche workshop manual schematic.

Terminals #7 and #8 on the 80 3.0L are empty so for now I won't fret about it. I'm assuming the black w/ purple tach wire is somewhere in the 76 engine compartment and I just need to jumper it (or rather extend it) to terminal 12 on the 3.0L 14 pin connector?

Undo the tape from the 14 pin connector to the CDI connector. Pull out the purple/black wire from the 14 pin connector. Move it to the T2 connector of the engine harness where a brown/red now exists. (Beside a red)
You’ll need a .250 latching female spade terminal.
Eliminate (tape off) the brown/red wire as you don’t need it with carbs.
Tape it back together and done.