I recently purchased a used, lower unit assy for a 3.5 outboard. My old lower unit had a water intake pipe to feed cooling water to the piston head. The "new" lower unit does not have a water intake pipe, or any structure to accommodate one (e.g., no interior mold recess, no guide holes out of the exhaust rear, etc.).
See this link for a comparison picture:
http://oak.cats.ohiou.edu/~bg101597/KB_lowerunits.jpg
Is this a special lower unit made for an air cooled powerhead? Can it be rigged to take a water pickup tube? Other options?