Or industrial application.
The extra port could be to feed the water-heated crossover under the carb in industrial motors. And *I think* there were differences in the industrial/marine timing covers as well (mounted the pumps higher).
If I remember correctly, some of the early (ie poly) units didn't even use a harmonic balancer, so pump clearance may not have been a consideration.
Could some supplier have pulled an old Industrial/Marine foundry master out of storage and begun using it for passenger applications, not aware of the differences? Just speculation on my part.
