UPDATE: From Roger
The Bart Markel picture was taken at the 1971 Charity Newsies Columbus, Ohio half mile, I'm pretty sure. When the race stopped running it's place was taken by the Lima, Ohio National. Bart finished 32nd in the points chase in 1970, hence the #32 for 1971. Otherwise, he was #8 in the early 60s and #4 for the rest of his career, not counting his Grand National Championships of course. This link shows Bart in the same leathers in an AC spark plug ad from 1972. (scroll down a bit for a bigger picture). The bike and handlebars look to be the same, and may have been taken in 1971 for all we know. AC Delco is a big General Motors (GM) parts supplier and he worked and lived in that same Michigan area, so he would have been a natural for them too.