I haven't been back to the marina to look at the fuel pump and see if I can detect the overflow tube being filled with gas. Exactly what am I looking for here ?

Isn't the mechanical fuel pump on my engine the same pump that was previously mounted directly to the block at the fuel pump boss only now mounted to the Mercruiser belt driven adapter ? If I do need a fuel pump where's a good place to purchase this pump ?

The arm on the sea pump mounted fuel pumps is different than for a block mounted fuel pump.

If it is the pump look for Airtex 60932, they make the Merc pumps
Airtex Fuel Pumps » Single Product - Airtex Fuel Pumps

Mechanical fuel pump spewing gas directly into manifold from overflow tube. Problem solved.

Thanks for all the input and advice.

Awesome! Thanks for the feedback and closing out the mystery. Post #8 wins! Lol.