Another week down and a couple new additions to the 912. I'm driving it every day now, and the car's loosening up nicely. It's a lot of fun and gets plenty of stares (maybe because it -looks- so old with this paint being flat etc.)
The whole time, I've been driving it with the interior gutted to bare metal except the dash and driver's seat. Since all the rust scraping and brushing was now complete, I finally had the time to apply the Eastwood 2-part rust converter.
You take 4 parts of one solution (resembles slimy, thick kool-aid) and mix it with 1 part of the wetting solution (resembles alcohol) and stir. It looks like thick purple paint when you're done mixing. I used a spray can cap for the measuring tool.
I used a tiny foam roller and tray ($3 at Walmart) to apply. I went over every bit of rust and most of the painted stuff too just for good measure, applying a really thick, wet coat. After an hour or so I applied another. Within minutes, the rust begins to turn black.
I did about 1/4 of the interior at a time, and it took ~3 hours to do the whole interior.
Half-way done:
A couple hours later, the rust was now all completely black, as black as death. No rust dust comes off it, etc.
It's pretty neat stuff because it starts out gooey and sticky, then over time it dries up and it only affects the rust. The areas with some leftover factory paint don't change colors.
It's been days now and the interior finally has no more rust smell. The next step is the Eastwood rust encapsulator, which will coat everything in a rust-sealed paint with a heavy top-coat, then I'll worry about any leftover small holes or areas that need patching, such as the back seat cushion area before I start the carpet and interior repairs.