I strongly suggest you enjoy the car for what it is, keeping it drivable for as long as possible, getting the mechanicals sorted, before pulling the thing apart. I also wouldn't change anything but body bits and
maybe some interior on that car. It's lovely as-is. Worst case, we're all ready and waiting to buy your car if the project takes a bad turn, and the stock parts if it doesn't.
I myself am on the precipice of such a backdate in no small part because my car already has a lot of aftermarket bodywork that I don't love. I have no plans to change anything but the bumpers, hood, decklid, and add some bits to the fenders. I would try not to cut any metal on one of these cars, unless it bolts on and you have an extra one lying around.
To that end, reversible, bolt-on backdate that looks fantastic:
Light weight image change - Body Overhaul Projects - Impact Bumpers
I dunno why anyone would bother with originality when backdating a car. It will never be authentic or original. It's an hommage, not a counterfeit. If it looks good, it looks good.
But of course...there are enthusiasts for all manner of pristine and ratty classics. Do as thou wilt shall be the whole of the build. $1,000 hood emblems. Christ.