Hey CD,
I had pretty much the same boat...
except mine was an I/O.
I just sold it a little over a week ago. Mine was a 1968 and boats from that era were from a time when the builders didn't know or want to know how little fiberglass they could get away with using so it is definately overbuilt. I did some real wave bashing with mine and I remember thinking to myself how solid it seemed. I mean there was no pounding sounds or the kind of resonance you get from thin 'glass shaking around in lighter boats. I think that you can get away without putting wood back in there.
I really didn't have any complaints about the boat. I just found it a little cramped for my family of five, plus I wanted to bring along a couple of friends now and then. For it's size the boat is narrow by today's standards. If you notice in my pix the hull is well within the fenders on the trailer. A current runabout would extend out over the fenders by quite a bit. I think I measured it once and the beam was shy of seven feet. The narrow beam makes it a better sea boat but it does cut down on the elbow room too.
Something I always wondered about but could never figure out... maybe since you've got your's opened up you can answer this for me? On mine there didn't seem to be any way for water to get from the bow to the aft bilge area. The bow had an inner liner that made up the forward cabin vee berth and a footwell that extended out into the cockpit. There was an anchor locker in front of this liner so it was possible for water to get under there I guess, but I couldn't see how it would get out. Looking at your pics doesn't make it any clearer.
Good luck, it's a worthwhile project for sure.
Steve P.