Its all about the keel
For 1978 you will have a solid cast iron keel rather than the older welded plates with fglass covering, so you are already ahead. And it will be easy to examine its condition if the boat is out of the water. The keel is about the only irreplacable part of the boat, but other problems would of course cost money, time and effort.Along with the keel, the pivot pin, its holes (where it goes thru the fiberglass) and the entire case (keel slot) should be examined for damage and signs of stress. A bent pin should be replaced (not difficult). Often the holes get elongated with years of wear. Because the area is fiberglass, its fixable but involves removing the keel. The keel winch and its wire for lifting the keel are important, but very replaceable.As with any boat, look for hull problems like blisters, delamination and major cracks. The hull is thin but well made. If its on a trailer, some flexing near the bunkbeds is frequent, but should disappear in the water. The rubrail and deck/hull joint are obvious areas to examine for damage. Some minor gelcoat crazing is to be expected around the deck fixtures. The rig can cost money to fix, so take a good look. Problems with the mast may be a deal killer, but other things are replaceable. Wires that are kinked or have fish hooks need to be replaced. In fact, it's advisable to replace all the rigging at this age or at least do tests for invisible corrosion. As someone said, sails are expensive so good ones are a plus. Originals may be nearing the end of their life unless they haven't seen much use. Used sails are an option here.The rudder should be the original kickup design; its condition will say something about how careful the owners were. Its another unique item but I understand there are places that can supply them.Wiring was always rather pathetic so plan to do some upgrades. If there is the sliding galley cabinet, dump it. Plan on buying a new portable head (who wants someones old one). Extra equipment is great, but usually too funky to keep unless the PO took good care. Good luck, they are a really fun boat.