[rcnight]

I had a soft spot in the forward deck. My boat is a '82 and it used plywood blocks for the core - the same thing on my '79 tank hatch. The blocks came apart very nicely which made demo easy. I think you'll find it was common practice - I don't recall any mention of balsa being used. I think there's some good threads that will walk you thru the repair process - pretty easy stuff. I'd use epoxy so you have longer lay-up time & better water barrier. Good luck.