I don't think you can get a new wiring harness. However, I would suggest you go to a junk yard and get one off a 302 there. As far as the ignition harness goes, you could get one off a 351 also, but you would have to extend the coil connection. Better yet, forget the Ford ignition harness and install a MSD ignition system which has it's own cables.
If you get a Ford harness, it will directly plug in the same place as your old I6 harness. I just installed a MSD system and it is a lot better than the old Duraspark II system. My engine has never run so smoothly.
Good luck,
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