mechanic

No no no. Do not go buy a head from O'Rielly or any other auto part store. Call auto salvage yards and find your engine. If you have the room I would buy the whole engine even if it does not run. Junk yard pull engines are cheap because they are just dirty cores. Then just take the head or heads you need and sell the rest online. Or just get the head and get it tested and rebuilt at a machine shop.

First step is to take the heads off and look. It could just be a gasket. But when the head is off take it to a machine shop NOT A MECHANIC. A mechanic will just take it to a machine shop and charge you more. If they find a head is bad ask them the best place to find a head cheap. They might just have one laying around. Then check junk yards. But if the heads are good then just go get top of the line gaskets and put them back on. Cheap gaskets can end up costing you an engine. I go cheap on lots of things but not gaskets.