The engine work was done by my friends Dan and Nick at Wyman Boathouse & Restoration LLC (they're also on Facebook). Its a 1965 Mercury 900. I believe its the first 90 HP outboard engine that Mercury made. Its an inline-six cylinder engine. The old Mercury family of inline-six outboard engines were nicknamed "Tower of Power".
The engine had good compression and ran, so it was a good candidate to be restored. But parts can be hard to find. Dan and Nick, a father/son team, tore it down, sandblasted and repainted many of its parts. They also cleaned/degreased the engine block, and then reassembled the engine. The only significant work that needed to be done to the engine itself was rebuilding the fuel system. Other typical maintenance work included new timing belt, new spark plugs, and a new water pump.