Engine decking issue(help)

machinists are human, they can and do make mistakes. Sometimes it's the machine, or setup procedure, or the machining technique. It can also be poor training, carelessness, even ignorance.

But a high-zoot machine does not guarantee superior results, or even acceptable results. I once was tasked with diagnosing running problems for a freshly rebuilt 383 4bbl. It had unusually low vacuum, considering the combo. It turned out the valve seats had been cut with a Serdi form-cutter. At first blush, they LOOKED perfect, but in reality, they were not square and concentric with the valve guides, so the valves weren't sealing properly. So I redid the (then)state of the art" cut valve seats, using my (then)50 year old old-school seat grinder. Problem solved.