Join Date: Jul 2006
Location: Galena, Illinois
The bolt holes are identical on 750, 101-1300, 101-1600 ........ a while ago I created a metal template that just fit the 8 hole ........ I tested it against the 750, 101-1300, and 101-1600 cylinder head studs ...... all the same.
My 42 and your 41 could easily be explained by the tolerance of these basically handmade manifolds.
Your 420 to my 435 is a big variation .......... so maybe yours is a real 750 and what I have is really 101 ....... just by the assumption that as tight as these fit against the body, Alfa would have made later ones bigger; not smaller.