The first step if you don't totally know the history of the heads is to see if the valve seats are banged up. If the person selling them to you ran the engine after it happened they must have taken them apart, done a valve job, and reassembled. You or a local shop can dress them up. If someone walked in my shop with two heads looking like that and I didn't have to pull them apart I would charge around 100 dollars if they did the after work cleaning. You can do it yourself for less than 20 dollars.