There are several part numbers for the 4:2 cast iron exhaust manifold; various 128's, early US X1/9, Euro spec X1/9, and all of the other Fiat models with the same head configuration. The manifold spans a number of years and models, each with variances accordingly. Has anyone found either a listing of those part numbers and what they come from, and/or any specs on any of them (i.e. port diameters, collector diameters, flow values, etc)? Any information is appreciated. I've reviewed Steve C's classic SOHC document, searched the forum, and Googled it several ways. The most I can find are vague references that some are better than others.