Manifold EGR Jets

Well if you're gonna have to run a tap thru those holes anyway you could go to the next closest convenient size or even ream it out a bit to the next appropriate tap size.
Good chance it's plugged up beyond what can be seen, anyway. If you do thread something in there be generous with red loctite/
Maybe the /6 is different from what was used on other engines? Or ones with an EGR are finished different?
When floor jets were used that was the original EGR before they had àn external EGR valve.