Welcome!
I just used “steel wheel” paint. Some brands are lighter or darker. Pick what suits yourself. I prefer a slightly darker shade myself.
Welcome to the forum!
Please do tells more about your S1!
I have an S1b (601) that was fit for the scrap heap when I got it. I didn’t do a restoration but more of a resto/period-mod using pieces available in period such as a crossflow engine, 5 speed transaxle, etc. I also built it as a driver and have driven 20k+ now. I love it.