the casting on the manifold should be X code then, if it's a real experimental. all experimental Ford parts are marked with an X casting number. would be XD6 I think, meaning experimental 1966, because all Ford engines at that time and maby still are, backdated 1 year, so the engine is actully a '66 if it's original. X= Experiamental D= 1960 decade 6= 6th year.