You'll probably have to replace all lines and rigging, unless they have already been replaced recently. However that's expected on a used boat. Then there's the tramp and sails, check the stitching and overall condition. Depends where the cat is located and if it was exposed to the sun a lot.
Take a good look at the mast to make sure its straight and doesn't have any dents in the lower section. Inspect the comp tip for cracks and any deformities in the sail track.
Then there are the hulls, check the area around where the cross beams fit into the hulls for stress cracks or excessive play.
Last item I can think of is the rudders, check them and the castings for cracks, you might have to either adjust or replace the cam locks. but that's not a big deal.