Is there evidence of the keel separating from the keel stub (exterior view)? Catalina used plywood in the keel stub until the late 0's. When the plywood rots, the keel bolts drop. Look for unusual depressions in the bilge around the keel bolts. This needs to be fixed.
Is the mast up? If so, look for the margins around the head door. Are there signs that the deck and column support column are dropping? If so, this could signal that the keel support (at the forward end of the bilge behind the bilge fiberglass wall) is rotting. Not a show stopper- many solutions posted on line. On my pre-sale inspection, we were able to probe the keel support block thru a small hole in the bilge fiberglass front wall revealing a completely rotted support block. This needs to be fixed.
Is there evidence of a deck compression at the mast? If water leaks under the mast support casting, the deck can soften and compress. This needs to be fixed. If mast is up the sign is that he turnbuckles are fully "used up"
Look for water intrusion signs at the side ports. This is fixable but can be a pain. Catalina did cutouts manually and the openings can be irregular leading to leaks between the exterior fiberglass and the aluminum frame - many fixes posted on line. With a boat this old, it is also possible that the rubber extrusion "U" seal between the acrylic pane and the aluminum frame may be degraded. Don't think the rubber extrusion is still available, but this too is not a show stopper.
Good luck. Let us know how you make out