SE216 (Replaces Most Mercury 3.0L) 

SE216
Replaces Most Mercury 3.0L Lower Units
13 Splines
20, 25, and 30 inch Shafts.
If you have an 8 Spline drive shaft you will need to buy the stub shaft unit
and purchase an upper driveshaft from an OE dealer.
20" 45-824114A 1
25" 45-823901A 1
30" 45-824115A 1 (This item is no longer available from the OE. You will need to source a used one, or fix your old drive.)
If you have a 13 spline two piece shaft just purchase the appropriate
one piece shaft.
The SEI 216 gear cases are supplied with the correct water tube coupling for units with a serial number of OG438000 and higher. If your unit has a lower serial number, you will need to use your old water coupling or purchase the correct part (SEI part number 96-116-12K).