For overheads, Serves, and Volleys, most people use a continental grip (hammer grip). When I used a eastern grip while doing overheads, I found that the balls often went long. By switching to a continental I added more spin, and could wack the ball hard without it going out.
Switching from a eastern to continental is not difficult (in a game)
Continental-V should be on the side of the racquet. You should be able to hit the ball with the edge of your racquet.