Gary,
Your 28+ deck has a balsa core. It's the newer 28 (which began production c. 1985) which has a foam core, and it might have been only the first few of those.
I noticed that the E32-3 owners' manual has an illustration indicating a Divinycell foam core in the deck. I don't recall that foam was ever used on the 32-3 but I could be wrong. The earlier 32-3's certainly had balsa. Any owners notice a foam core?
-Roger