Need help and advise on valve adjustment with non adjustable rocker arms & shaft

Rocker geometry is not the same as pushrod length. The two are dependant on each other because the valve stems are leaned in slightly towards the rocker shaft. So when you raise the shaft, you effectively move the rocker's contact point towards the outside edge of the valve stem.

The valve job is crutial to proper rocker geometry with a shaft rocker system. If a shop sinks valves without reducing the stem length, or can't get all the seat heights in the same spot, you will have rocker/geometry issues. If the heads or block are milled or the head gasket you chose is different from the factory, the pushrods will be a problem. The right way to solve a pushrod probem is new pushrods. The right way to fix a geometry issue is have a good shop do the valve job from the get-go.