Engine decking issue(help)

The various manufacturers offer CNC packages for their mills. But it's pricey and unless you're doing production work may not be of any value to the shop. Purchase of this type of equipment has to bring money in, or it's not going to work out.
In terms of accuracy, the older stuff cannot match the new stuff. Period. I don't care if Jesus himself set it up, both design engineering and years of service makes it so and the fact they don't own equipment precise enough to measure to that degree does not mean they can equal the output.
There's reasons why some engines are better than others - the foundation is the block, and the machining of that is the forming for that foundation. Y'all can wish all you want. You can expect all you want. You can appreciate the oldschool and expert labor. But as Scottie says - "You canna change the physics!!!"

Nasa doesn't use slide rules anymore. Mechanics don't use dwell meters anymore. Ships don't use sails anymore. Evolution... it's real!