1966 Barracuda

The Commando pistons should work fine. They will have 2 valve reliefs, and the lower compression pistons will have 4 valve reliefs. Unless Cometic makes a really thin head gasket, .028 is the thinnest gasket I have seen advertised. The factory gaskets were thinner than that, I think? The intake you ordered will work perfect on the late model 302 heads, but you can easily make it work on 64-65 273 heads if the ones @pishta has are good. You can file the holes in the intake, and use wedge washers under the bolt heads. If you do end up buying a set of 302 heads from Rock Auto, you should still take them to a good machine shop and get them checked. You may need to get valve springs to match your cam, and get a good 3 angle valve job done before you put them on. Good luck with the build. :)