Looking to get new cylinder heads for my 4.3 since my #3 exhaust valve is sticking open during heavy loads. How many different heads did the second gen 4.3 have? I want to get heads on order before tearing down the engine. Or is there an easy way to check head casting number?

Thanks!

Edit: More info on my issue. Definitely acts like the valve is getting stuck in the guide. After doing a hard pull up a hill I lose compression on that cylinder and you can hear it puffing out of the exhaust. After driving normally for a few minutes it will close and stop misfiring.