The existing harness will work fine. you will just have relocate a few wires like the coil, idiot lights and starter. If you leave the altenator on the left, it should be ok. Otherwise, it will need to be relocated as well.I'm pulling a 230 6cyl out of my 66 nova...Swaping it for a 327....Is it absolute that I need to change the engine harness????..Or can I get by with the exsisting wiring..???.......Thanks