Back to the Summer of 2014: When I first looked at the car, I took copious photos, as anyone would. The following image shows the underside, from front looking backwards. The front suspension pan was all rock solid, not even surface rust, but the fuel tank and had some nastiness nibbling away at it. (You can also see the disassembled engine, on a bench beneath the car.)
Once in my ownership and home, my approach to the car was fairly disciplinced, mostly due to a lack of cash. I'd decided to do everything except the engine first ... that would require some planning ... and to try to stick to one system at a time. It was the first 911 I'd worked on, save for some help I'd given my local bud Paul with his red 930. I started with the gas tank. Fortunately, it was in good shape internally and didn't require any professional cleaning (my 924S's gas tank, in comparison, was in dreadful condition internally and required professional help).
I stripped the lower half with wire cup brushes on a 4.5" grinder. This, for the uninitiated, is an activity that
begs for first-class personal protective gear. I WAS wearing eye protection but NOT enough protection on my torso and legs, and recall picking strands from the wire brush from belly and limb, many of them shockingly deeply embedded. (Thank science for tetanus shots.) The upper half - which obviously gets to live "indoors" - was in nice shape, so I just washed and prepped it thoroughly for some cosmetics.
Once the lower half was stripped bare, and satisfied that the seams joining the two halves of the tank were still ship-shape, I primed it. At that point in my restoration knowledge I tried POR15 for the first time; I don't use it today, but the tank has held up fine in the intervening years.
Once the POR15 was fully cured, I scuffed it with red ScotchBrite pads to provide a key for the following product. That was a grey, paintable rubberized texture coating to emulate the factory-applied Schutz. I used UPOL aerosols, which worked well, but probably wouldn't satisfy a concours judge (not my goal). Still, it was pretty good.
I can't find any phots of the final steps, which were, a) to paint the whole thing; I used "Machine Grey" Rust Oleum, applied with a small roller, and b) to install the tank with a new Genuine Porsche closed cell foam seal. That installation, however, happened some months later, after I'd R&R'd the steering rack for a clean, new bearings and regrease, and replaced the fuel tunnel lines. So it went into the basement, ready and awaiting its repatriation with the car.
John