I was watching an old baseball game on the MLB channel a few weeks ago. I think this game was played in 1952. The manager of one of the teams was also coaching 3rd base for his team. Would that have been a common thing to do in 1952 or anytime?
Managers did take on the role of third base coach (or rather, did what is now the job of third base coach) early in MLB history, though by 1952 it would have been more rare. See this wikipedia entry for example:
By the 1920s, most Major League teams had two full-time coaches, although the manager often doubled as third-base coach and specialists such as pitching coaches were rare. After World War II, most MLB teams listed between three and five coaches on their roster, as managers increasingly ran their teams from the dugout full-time, and appointed pitching and bullpen coaches to assist them and the baseline coaches. Batting and bench coaches came into vogue during the 1960s and later.