50chevy,
Goodmark makes and sells a large variety of patch panels for 67-72. Like Mechainiac said, you can also get them from LMC or any number of other dealers. Some of the dealers carry the Goodmark stuff but some carry Taiwanese products that are less than first-rate quality.
As for removing the gas tank, if you're just replacing cab corners or rockers, there's no need to take the tank out. For the cab corners, just put a heat shield in front of the tank and you'll be fine. Of course, if the gas tank's leaking, that's a different story -- take it out! It's not hard, but kind of a pain. You have to remove the seat, gas lines, vent lines, electrical lines, and fuel neck grommet. Oh yea, make sure it's empty first.
