Sullivan was a boxer before turning to music, perhaps to avoid the burden of expectation that would accompany such a prestigious pugilistic appellation.
This flyer appears to be a promo for a tire company in Lubbock (the floating tire is obviously superimposed on a photo of the musicians; one can only guess at their relationship to the company). According to the bio, they worked radio stations in Fort Worth and Lubbock, so it's safe to assume that they were well known in Lubbock at the time this flyer was produced.
The duo formed in 1939, which seems to correspond with the general vintage of the collection of the miscellany I've been scanning and posting on this site. In 1941, they recorded "When My Blue Moon Turns to Gold," which Elvis Presley turned to money when he recorded a pop version in 1956. Here's a recording of the original version, courtesy of YouTube.