Thank you Stan! This is the first time I've tried flat tires. There are a few tutorials on here and I tried their techniques. I'm sure I'll get better at it.
I started by sanding the tire to get it rough and worn looking. Then I used a small hand saw to cut two vertical cuts into the tread along the inner and outer sidewalls, not quite all the way through. The with a small razor knife, I cut across the tread to remove the section between the cut lines. After than, I held the tire over a lit candle to heat the rubber, and pressed it onto a hard flat surface to flatten the sidewalls. This took several attempts. I ultimately headed the blade of the knife and used it to shape the rubber to spread the sidewalls out so they would stay in place. Kinda like frosting a cake. I'll try to get some pics of the process next time I do another flat.
The result is more like a tire that's rotted from sitting, rather than simply gone flat from a leak.
Your abandoned Impala is looking really great!