Re: Force lower unit identification by the cast number
Right around 1989, Brunswick (Mercury) started changing lower units a bit with different water pumps and gear ratios. While they all look basically the same and until 1994 or so all were interchangeable between any three, four, and five cylinder engines, parts for each particular lower unit were not.
Physical size for all units is the same, but gear ratios can be 1.76, 2.00, or 1.95 depending upon engine and internal design. You can find out this by turning the drive shaft 2 full turns and noting how many turns the prop has gone.
If your lower unit has dual exhaust with the water intakes being six holes running up the side of the leg, then it is the newer model with a 1.95 ratio and a Mercury type water pump.
So, post a couple of good photos of the lower unit and perhaps we can identify it for you.