Hard to imagine where the $70k went, but it's possible when you go nuts on stuff. Unfortunately, 66-67 Chargers just don't bring the bucks. You can buy a nice driver for less than half of what is invested so far.
I think you are looking at a max of $20k, and that is for someone someone who would go through all the boxes and really spend the time too see the value in the restored parts. If it were mine and was giving up on it, to improve the sales price and widen the buyer pool, I would weld in the floors and assemble it as much as possible.