They changed to dual timing chains in 84, but there was a service advisory and Merc updated a lot of the older ones when they were a few years old. YOu have to make sure it's been changed. The single timing chains are fragile, especially after all this time. I have an 84 380SE. It's not fast off the line, but it's fast enough. On the highway, it's plenty powerful and glides along at 80 mph all day long. My mileage is in the high teens.