Where's the Rocker Pedestal on 1967 440 915 heads

The valve cover rail is not a machined surface. I would think the measurement from it would vary widely with different casting dates and numbers. If you set the head, gasket surface down on a surface plate and bolt a rocker shaft on to the end pedestal using one of the center shaft holes, so it hangs off the end of the head, you can then measure from the shaft to the surface table using an inside micrometer.