Mr. Houston's home is the same home used by Jonathan Hart in Hart to Hart, the famous home of Dick Powell.
Betsy's car that Clint is working on is an REO. This was the car company Ransom Olds started after he left his first startup, Oldsmobile. Due to a legal restriction he could not use his name in any new company he started so he simply used his initials and the company's name was pronounced as "rio". One of their early designs was what was one of the first prototypes for a pickup truck and was called the REO Speedwagon, the source of the famous 1970's rock band's name.
During it's long run this show would recycle various plots points. This was the first of several stories where Mannix is "hired" by a child.