I'm drilling out the #5 boss for the ACT sensor and the boss on the passenger rear for the EGR coolant return. Are both holes the same 3/8" NPT thread size? I did a search and didn't see the size for the EGR hole.
I wish I could remember to help you... but do you have both parts in hand, and maybe something to thread them into?
If you know the one for sure, drill and tap it, then try the other component in that hole. If it threads fine, drill and tap the other hole the same. Without knowing for sure, I would just use a process of elimination and/or comparison between the parts being threaded into the intake to make sure. I wish I could be of more help.
JUST BE CAREFUL!
The soft aluminum and thin nature of the aluminum at the ACT boss will not be forgiving to cross threading or forcing anything. I noticed that with mine anyway. Even with the boss, that aluminum is aweful thin.