Heads, how much gain?
It's good practice to have them checked and corrected. You can now buy barea castings, or assemblies, so if you can work with a local guy who's good you should be able to get out of them for less than $2200 ready to run. You also need the right gaskets and the right head bolts - so be aware of that. In terms of out of the box performance - with a good valve job the RPMs will outflow factory iron by 5-8% depending how good your iron is. A decent amount of that it low lift flow, so I'd expect some gains - feelable gains - with no other changes. plus you're taking 80lbs off the nose which will give more of a punch to the car with no additional power. In terms of power numbers - around 4-5% would be what I expect assuming not other issues and solid tuning. Your results may vary...lol.