As above, oversize the two right-hand side holes to allow
1. Drilling access,
2. tapping access,
3. Screw-tightening access for assembly
4. Screw-loosening access for maintenance later.
BUT! replace the medium-sized center hole of the two RH ports with a 8-bolt pattern further away from the center of each hole (now, you have 8x bolts, but in two bolt-hole circle diameters - one inside the other.) The "port diameter can be the same as now, but the "port" diameter is set by the piece being attached, not by the drilled hole in the housing that is pictured. If it is absolutely essential to maintain port hole diameter and location of the nozzle outlet into the housing, change the attached piece so it matches the current diameter, but has a deeper tip. And, of course, the 8x bolt holes matching the 8x tapped hole in the housing.