TS you haven't missed anything, I haven't finished the other version yet.
So, maybe this is a day late and a dollar short (so by all means ignore me, if you want)...
Why not just do a two-piece per side part (from the start), with the rim/frame having 6 or so screw posts, and a separate grill that attaches (with screws) to the rim from the rear? This would have multiple advantages:
1. Only one (set) of CAD files
2. The ability to easily sand/finish both the frames AND the flat surfaces of the grills far more easily than if combined in one single piece. (Especially useful given the 3D printing process can leave build lines everywhere.)
3. The ability to more easily paint in contrasting colors (if reqd).
4. Allows the use of a different grille material OR the ability to
move to a different grille material later, if wanted.
Advantage number 2, I think, is especially important!