A would be out to the filter. B is the inlet back to the main galley. That small extra was added. It is in common with the main galley, so it could be a feed to something external(turbo/ supercharger, oil accumulator, or as some guys would do, plumb it to the oil feed taps on the rear of the block)
Or it could be an access to bleed the miserable thing everytime it looses its prime

"use it 'till it breaks, replace as needed"