Engine decking issue(help)

It's the Indian and not the arrow. You need equipment and fixtures that is in good shape and repeatable, but after that the success of the operation is in the setup and a CNC or digital displays won't compensate for insufficient attention to detail. As pointed out, they've been building high precision engines and other crap long before the current crop of machines came out. The new stuff makes the machinist more efficient/productive, not more precise.