Golf club heads (e.g., drivers, fairway woods, wood-type hybrid clubs, or the like) according to at least some example aspects of this invention include: (a) a heel; (b) a toe; (c) a crown; (d) a sole; (e) a striking face; (f) a cavity, wherein the cavity is at least partially open; (g) a rear face opposite the striking face, the rear face defining an opening to the cavity; and (h) a rear body member configured to be inserted into the opening. The rear body member may be releasably engaged with the opening to the cavity, rear face, and/or other portion of the club head body.