Check the capital yachts
website, but I believe it is solid with a few areas of foam core.
"The Newport 27-S is built by the hand lay-up foam core and fiberglass method."
Newport 27 Bochure
I've installed a couple thru-hulls in my 1976 Newport 27 (granted, not a 27-S), and the plugs that came out didn't have any wood coring material.
I'm sure the construction varied from year to year, but I would be surprised if they suddenly decided to start coring their hulls with balsa.