Look at the bellhousing. If its the smal housing then its a 351c, if its a large housing then a 351m/400. You can also measure across the intake, the 351c is smaler than the 351m/400 but I dont recall the measurment of either and I'm to lazy to go out and get the 351m/400 measurment for ya..lol. Maybe I will feel like it later.