Could you post more pics of the aluminum in the crossover port in the heads? I have never heard of this. I am building a 340 and would like to do it to my heads also. Cool build, the car looks good.
Here are some more photos of the melted down piston in the crossover port. We took a iron plate and bolted it to the side of the head that meshes with the intake manifold and then we lay it on that end and pour the molten aluminum into the exhaust port up to the chamber so that it matches the other exhaust ports. You want to make sure when you do this that you do one continuous pour because the aluminum cools very quickly and if you stop and start you can end up with two layers of aluminum which are much weaker. If you pour too much you can always take a die grinder to it. After you have poured the aluminum you can take the die grinder to fine tune the aluminum to match. Unfortunately I didn't take a photo of the exhaust crossover valve before I filled it but here are some photos of a regular exhaust port and the one after we filled it will aluminum. They will flow much more consistently and its a good trick to pick up some horsepower at higher RPMs.