BEJ

Quick question that hopefully someone can answer. I am looking to replace the ignition wiring harness on my 75. The car came with automatic but I have swapped the auto for a 4 speed. I replaced the dash harness a few years back, but installed the 75L auto one. Is the only difference between the auto and manual ignition harness the wire for the transmission (auto)? Would it make more sense to go ahead and just replace the ignition harness with the auto one, or would it be ok to replace with the one for a manual? Ok, so that was more like 5 questions but I appreciate any advice you all can give.

Thanks,
Bryan