How much decking is to much?

Find a new machine shop.

What's the machine shop(s) have to do with the block not being square from the factory? I am talking about two 340 blocks that were decked at two different machine shops (about 1,500 miles apart from one another) where they both found the same discrepancy, namely they found the passenger side deck was higher than the driver's side deck (and neither would clean up after the first cut). We measured the piston deck height's before hand and knew the problems going in.