The distance from runner divider center to runner divider center on my Early casting TF heads is 9.585. I am using the Fel Pro gaskets 90175-1. They and the valley pan measure as you stated. The gaskets openings are slightly larger then the tin valley pan. Putting the gaskets on the head numbers out to the intake manifold side they line up good with the gasket overhanging on the top. If swap the gasket and turn it numbers in, it is shifted on the ports to one side.