I've had several Cal's and none of mine were cored hulls. I'm
nearly positive that the '67 c-24 is not either. There are two places
that they were built, Jensen mar Marine in Costa Mesa, CA and somewhere
on the east coast - I think up near Jersey. I've never seen a Cal
older then 1978 get a single blister either. In 1978-9 or there about,
Bill Lapworth sold Cal to O'Day and they in turn sold to Catalina.
Those are completely different boats and should be avoided.

The Cal's all have cored decks. They are a sandwich of glass and
balsa. I would check around the stanchions and around the port lights.
Also, many of the cal's have had their travelers placed across the
seat/step that is astern the companionway. The screws tend to stress on
those and let water in. You can feel a soft spot when you walk on the
seat if there is water damage. The portholes are a strong plastic but
by now they are old and will crack easily. The stern port lights are
pretty good but the windows fog. You can use a cleaner to get them
mostly clear.

The real problem with that boat is that you will need to add a lot of
stuff to get the creature comforts up to modern standards. Also, you
will probably need to change out an A-4 that most of them came with. If
it has been used very much the engine will cost more to keep up then
makes it worth having.