AMD has been stamping their parts in Taiwan for a long time. Not sure if they were always stamped there, but, that's how its been for years. They're still the best replacement panels for fit, and they bought up a bunch of the original factory tooling.
AMD has been known to make adjustments to their tooling, they have fixed things based on reports of fit as later runs of parts were done. Not sure what generation of stampings those rockers are, but "first run" parts usually require more work than later stamping runs.
But here's the thing, you say the floors, rockers, and quarters are "chewed up", and you removed the rocker. Those parts by themselves make up the majority of chassis strength through the middle of the car. If you didn't brace and cross brace the chassis before you removed the rockers, things could easily have moved.
The other thing is, the body tolerances on these cars have been known to vary by well over a 1/4" depending on the part/area being measured. No replacement panel will ever be a perfect fit for every car, especially almost 50 years later. If the factory parts and construction gave variation of more than a 1/4", you can't really expect replacement panels to do any better. Most cars aren't out by that much, but some are, and with as much damage as you describe there's no guarantee your car is still straight, even if it left the factory that way. Removing and replacing major structural parts is a high level fabrication skill, and the process required to fit replacement parts while keeping everything square is why paying a shop to do that type of work is typically very expensive. It's not a slap it on and tack it up operation, and in some cases a lot of modifications may be necessary to get everything lined up. It can be a lengthy process, and one that can be quite different from one car to another.