I would use the factory body harness for all things not engine/trans related. Use Holley's harnesses for your efi. Get a copy of the Holley main harness wiring diagram. It us easy to figure out from there.
Dart 348ci, Ed Curtis cam/valvetrain, Precision 76mm, Holley Dominator EFI, CNP ignition, tons of Holler EFI small parts, 4"dp, 4R70W w/T-brake, new suspension coming soon.
Little 750rwhp at 6,000rpms and only 10lbs of boost before we just got tired of playing with clutches. New 4R70W and we are turning it up. Expecting 1,000rwhp.