Essentially all by hand. I'd tried to do it a few times before with different quality scans, and while I could see the original intent on all of them, auto-tracing never held up across the whole poster.

I ended up taking a few days zoning out and re-drawing it as a white/black raster image over a highly scaled up scan, then auto-traced that in Illustrator and coloured it there. Text went in as some variant of Century Gothic with a few changes to match the original.