A up, when rebuilding my bsa engines I remove all dowels , pins, etc and with a sheet of glass large enough to take the cover check the faces for flatness. If a fine feeler gauge can be inserted between face and glass its a case of facing them using grinding paste on the glass using figure 8 pattern and patience. when a nice matt finish can be seen on all faces check with feeler gauges again, remember to remove all traces of grinding paste when satisfied
Wet sumping,I think, is a pre condition of owning old brit bikes, fire them up every week this helps the oil from free draining, check all balls seats, springs on pressure relief valves . hope this is of use. good luck