Re: A hole in the cabin top, what was it?
Those holes are the drains for your dorade vents. The S2 did not use the traditional boxes, but instead internally ran the drain within the cabin house. If you had a cowl vent instead of the solar vent, rain and spray would enter the cowl but would be funneled out of those holes instead of entering the cabin. You should have one or two holes (depending on design) port and starboard side (like you said), assuming the 27 had two cowl vents originally. Providing they have not been modified or damaged, there will should be no issue to the core material.
Rick