Pope has a good point. Early 289 was a positive stop stud and fulcrum unit. Were the studs changed out? If the OEM studs were retained, It's a possibility that the valve height wasn't compensated when the valves were ground and now the valve stem tips are too high. 62-68 push rods were 6.804" long. 69-85 were 6.886" long (non-H.O. & non roller engines). Possibly later push rods were used creating a .082" interference in length. There is not much material than can be removed on the heads during milling also. This can make the pushrods "grow" in their geometry especially if they were milled once before. Just some info to chew on.