No big deal, just get a new timing chain cover. They're on ebay al the time, and if you buy a timing chain cover gasket set, they come with a little gasket that will seal the part where the timing chain seals against the pan so you don't need to drop the pan and put a whole pan gasket on. You just take a utility knife or razor blade, trim the old pan gasket, and put a dab of sealant to seal everything together. It's a simple job, and once you have the old water pump off, the job's 40% done anyway. I had an exposed impeller on my old '65 fastback and it cost me a motor. Since the timing chain cover is part of the cooling system, and it's aluminum, it got a small pinhole in it from years of water and debris and allowed my radiator to dump about a gallon of coolant (and a tube of stop leak) into the pan, which is not agood place for water. By the time I discovered where the leak was coming from, it was far to late. If I had a '65 with the old-style cover, I'd swap it out in a second for a newer pump and cover, just for peace of mind.