Mercruiser: 48-816704A40, 48-816704A45, 816704A45, 876704A45 Shaft Splines: 13 Mercury 40hp (2- & 4-Stroke) (Not Bigfoot) 1977-Present; 40hp (Sea Pro/Marathon) 1977 - present; 45 hp 1986 - 1989; 48 hp (Mariner) any year; 50 hp (2- and 4-stroke) (not Bigfoot) 1977 - present; 55 hp (Mercury/Sea Pro/Marathon) 1995 - present; 60 hp (4-stroke) (Not Bigfoot or Sea Pro/Marathon) 1978 - present; 60 hp (2-stroke) 1978 - present; 70 hp (including Model 700) before 1983;   Force 40/50 hp 1995-1998 70 hp 1991-1995 75 hp - 1996-1998