Unfortunately, with all the tolerance stack-ups as mentioned, no one can guarantee that a head cut of .030" won't end up with pushrods too long. So cutting heads 10 times and not having an issue does not say if there will be issues or not on #11.
The above says why: different parts and different stackups. The same pushrods worked at the factory only because the nominals were the same and the worst case stackups were designed to work 99+% of the time. Once you cut the heads .030", you are well outside the factory nominal for head height and all bets are off.
As a design engineer in a past career, working with volume production designs and tolerance stack-ups, trust me.... Usually you are fighting to keep the fall-out to a minimum with standard parts tolerances, and costs make you loathe to spec tighter part tolerances. Put in a large variation like -.030", forget it; you are going to get some fair % of parts combinations that are not going to work together. That is why I don't agree with the idea of ever telling folks that they 'should not bother' on this particular matter.
