Miss-matched heads & manifolds?

Oldmanmopar said
This is the correct answer and couldn' have said it better. Plug the holes with 1/4 inch long 1/4 20 set screws . You can run a 1/4 20 tap in without drilling.

I will 3d that and here is cutaway to help understand.

a little hard to see with that tiny pic. left had side, just below the exh out let you will see the groove.