Mine is a 1973 model, all the cleats are thru-bolted with backing plates. The only cleats I can access and see the backing plates are on the bow and stern, so I really cannot comment on those amidships. The cabin top is bolted to the hull at 6-inch intervals and glued with 5200 (I guess that's what was used), and there is a lot of heavy, structural framing, which can be seen when you remove the storage drawers on the starboard side. However, I have no way of determining the fiberglass layup, mainly because it would be damned near impossible to punch a hole in the bottom of the boat, and don't intend on doing so.
Using a 100-percent jib, and battened main, I find the boat sails quite well in all conditions other than very light air. I'm too old to fool with a spinnaker or oversized jib (that's why I have an engine.) I'm sure that with some sail modifications the boat would point tighter, but I really am not in a hurry to do anything these days - I just want to put the sails up and stop in a quiet creek or cove when I feel like stopping.
When I was offshore and bumping against the Gulf Stream with an opposing wind, (my bad) the boat took the beating and continued to ride very dry in light of the nasty conditions. Once I got back inshore, the boat settled down and handled the 4 to 6 footers quite well.
The only negative is that with that close proximity of the prop to the keel is the boat does not back down well at all, and tends to do some weird prop walks in directions other than anticipated. I was thinking of switching to a 2 bladed prop to see if there would be an improvement, but right now I don't need the added expense, though I should probably have a backup prop on the boat just in case.
Having spent time on several Catalina's to 48 feet, I can honestly say the Morgan 33 OI has as much, or more, interior space and storage as most 41 footers. It never ceases to amaze me as to the amount of storage and living space this boat has. Plus, it has a very spacious cockpit and foredeck. What more could a cruiser ask for, especially at the price these boats are not going for.
All the best,