Shims are "bad" because they move the centerline of the rocker shaft. That in turn can negatively affects the path the rocker follows - they affect the geometry of the rocker. So you add shim to adjust for the wrong pushrod, and the rocker tip ends up riding slightly off in terms of it's path accross the top of the valve. So for the cost of pushrods you run the risk of wearing the guides faster, valvetrain instability, wearing the rockers faster, and wearing the valve stem tips faster.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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