[MadMax]

You could reduce a fair bit of material removal by using sheet metal for the uprights. Design them without the ridges at the bottom and get alignment from pressed in dowel pins at the top and bottom.

You also could save some material and total cut path length by nesting the shapes. Shapes spaced one cutter diameter apart would require less total cutting time because they'd share edges with common cut paths. Your machinist could set up a gang of parts by cutting all of the slots for say 20 uprights before cutting the outlines out and freeing the parts.

Screws should pass through clearance holes to deal with variances in screw nominal diameter. Drill four holes at each end of the upright. Two dowel pin holes, two screw holes. Ream the matching dowel pin holes in the upper and lower mid blocks 0.0005" smaller than the pins for a press fit. Ream the dowel pin holes in the uprights to the pin diameter or perhaps with a 0.00025" clearance. Precision reamers aren't expensive if you're doing a batch process, and they make much more accurate holes than drill bits. Drill the pin holes one drill size smaller than the pins (say 0.003" smaller).

There are also other schemes like using dowel pin screws. Look for screws with an accurately ground shoulder close to the head and a smaller threaded end. You can get the clamping feature of a screw combined with the accurate registration of a dowel pin all in one fastener.

Clearance holes in the uprights should be 0.5mm larger (handbook dia).

One other benifit of sheet metal uprights is that you can make common parts for either side.

If you use flat head screws (countersink type) you'll get a lower profile screw which wouldn't snag on a holster. Some of the more exotic holsters might hold pistols with attachments. The uprights would be identical right up until you did the countersinking pass which is an easy thing to change in CNC code.

For surface treatment, don't use powder coat. I goes on a fair bit thicker than anodizing (0.002" vs 0.0005") and isn't perfectly flat. You tend to get a bit of accumulation at edges and corners with p'coat which may interfere with repeatable installation of optics.