I am not sure how Bill got that manifold approved for the 273. It was probably some obscure memo or something in the parts book. You would not want the LD4B on a 340 You would want the LD340 which was a copy of the cast iron 340 manifold. I remember when most of the 340 SS cars used that manifold.
SS cars can run any manifold they want, and the ld340 and others are not like the out of the box manifolds at all.
