You want to do it right? Pull the engine, Transmission, the seats, the carper, the dash, replace the three harnesses, then plug in everything, like the factory did. The only way to do it the correct way. Anything else is just a hack job...IMO.
I have been very fortunate...ALL of the Mopars I have had have had beautiful harnesses. 68 RR, 68 Dart, 70 Cuda, 65 Belve. And I mean all harnesses. None cut or dicked with....