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)
But....
People helping on this forum didn't "come up with the problem", your engine did and you posted?
Is it okay that I'm confused reading this thread?