I'm thinking the excess is exactly this. Overflow/spill tube from fuel pump is dumping excess fuel from a ruptured diaphragm into the carb
OP has mistaken the air horn inlet/tygon hose for the bowl vent?
I'd start at the battery, starter and ground lead connections. Then the ten pin connection.
Guessing corrosion somewhere that was made better/worse with the motor r and r
Patina on the flywheel looks like a semi sinker at one point
Saved most of the running gear, ditched the transom assy and trim pump but kept y pipe, inner plate, p/s pump and actuator (old school greasable)