I only see one rocker arm where I think I should see two; maybe just hidden behind the outside one. But they look like they would benefit from going on a diet. Heavy cast steel? I realize you don't expect high RPM's, but that's reciprocating weight and without a lot of spring pressure, I can visualize them being lofted off the cam at higher RPM. Are the pushrods aluminum? Wall thickness, even solid, won't make them much stiffer. Have you considered thin walled tubular steel instead? I think they can make them any length you want and might be a good investment. As usual, we all like to make as many changes we can think of on the first pass out, which sometimes causes problems we can't solve. Walk slowly, carry a big Panther!