A "TV Guide" with Lucille Ball on the cover can be seen on the top shelf of the magazine racks, just as Mr Mason enters Walker's Drug Store for the first time. The Andy Griffith Show (1960) was produced by Desi Arnaz and Lucille Ball's company, Desilu.
Andy tells Barney that he could put the cannon in front of his house. Barney's house is never seen during the series and his only known residence is Mrs. Mendelbright's boarding house where he rents a room. It was also suggested in one episode that he lives at 411 Elm Street.
The actor who played Ralph Mason, the antiques dealer, was billed as Casey Adams, but was actually Max Showalter. When Showalter first arrived in Hollywood, Darryl F Zanuck decided that "Casey Adams" was a more bankable name than "Max Showalter" and that's how Showalter was credited until the early 1960s. Around 1962-1963, Showalter decided to reclaim his real name, using it professionally for the rest of his career.
The "park" where the cannon is kept was actually the expansive yard space to the left of the facade used for the Mendelbright house. It was not only the largest residence on the back-lot, but it had the largest grass area available to be temporarily dressed up as a small park.
Andy suggests that they try to sell the cannon at auction, but they try selling it door to door and not at auction until Mr. Mason buys it.