I have a set of gen vi 502/454 mag heads. They have about 150 hours on them with no salt water use. The motor never quit running so I don't think they have any problems. I bought a set of 2800 dollar Canfield alum. heads and a new cam. I have the heads, cam, rockers, keepers and valve covers if you are interested. They have never had any work done to them so they are bone stock. I know BBB said most of the used heads for sale are junk but I'll put my reputation on the line and tell you if you buy them and they are "junk" I will buy them back. With that said they are used and do have 150 hours on them, a valve could be in order? Or you could run them like they are. Those black motors have a lot longer life than 150 hours especially with only fresh water use.

Here's some pics, on one of the heads I wiped out the area around the valves so I could see the color of them.