I'm with the others in their recommending new (and that's what I sell too of course) but to your original question, there is almost nothing in common between a '70 and '75 Bronco harness. They made the major change between your year and the '71 model year, so almost nothing is routed even remotely the same.
The color codes match about 99%, but the location of components and the routing is about 85% different.
The ONLY way to refurb a '66-'70 wiring harness then, is with another one of the same vintage or new. A used '75 in good shape would actually be a nice upgrade in some areas from your '70, but just like the aftermarket ones, that means making a lot of changes.
Good luck no matter which way you go. You could contact American Autowire to see if their OE replacement division has an original EB harness yet, but I don't remember seeing one listed. I have not called them on it however, as most prefer to upgrade over original except for someone doing a very religious restoration.
Along the lines of restoration, even though the Painless is, like the others, in no way similar to your '70 harness, it's the only one that uses the original Ford wiring colors. All the others use the now-generic GM color codes. Not a big deal from a wire tracing standpoint, as they are all clearly marked as was said.
I will say that the less expensive Centech has the easiest to read wording from the ones I've seen. With Painless having the least easy to read, but with the proper matching color codes meaning that all wiring diagrams you might have are easy to work with.
Have fun!
Paul