There are a lot of those tracks still out there. I found a 1:1 dirt racing forum with Google Maps coordinates to a bunch of backwoods tracks. (Am I allowed to post the link here?)
The billboards came off an internet search for "vintage signs" and the like. Copy, resize, print.
That is a very cool track. Love the way it looks with those outside pics! The track reminds me of a dirt track I used to visit in Orange County NY when I still lived there back in the 1990's! Would love to see pics after some "rubber" gets down on the corners!!
I printed the signs on buff-colored cover stock. The thicker paper let me glue them on with 50% white glue with no wrinkling, and the slight color gave the white areas a little weathering. Then I sprayed cheap brown acrylic craft paint thinned with water through a $10 Harbor Freight airbrush for the "dirt" down near the track.