I have a new Melling M81 left over from a 4.2 build that I never did and am now building a 4.6 stroker out of a 4.0 block and 4.2 crank. I am not sure if I can use the M81 in my 4.0 block or not- I see different information in different places with some saying they are interchangeable. But a search of Melling's website shows only the M81a as being correct. I see no difference in dimension even though the M81 does look somewhat different. The oil pickup tube from the old 4.0 pump fits snugly and the new pump does not look to be a different height at that point so I would expect it to fit properly. The bolt holes are in the same place and of the same size so it bolts on fine. Any ideas?
