This modifies the top of the N Filter from PakRatJR's proton pack models by adding an inner ridge to allow the top part to lock into the lower part. This helps with aligning the two pieces and also is just about tight enough that the part can be held in place.
I also removed the material in the holes. The holes aren't perfect, but they are pretty dang close.
Print with the same settings you used to print the lower half of the N Filter, but use supports to help support the holes and ridge.