Each upright has four slats, with each having a set of evenly-spaced holes along their entire length.  Each hole has a counterbore, some on outer facing side the slat, and some on the inner facing side:

It took me a bit of head scratching to work out a good way to make evenly-spaced holes and also handle the counterbores on both sides.  I think I would have been fine with marking each of the 8 slats total at 80mm intervals and using the drill press to do the counterbores with a forstner bit first, and then going back to drill the smaller holes.  But I wanted something requiring less measuring and marking.  Hopefully, something less fiddly.

I decided on using a plunge router with a guide bushing to drill the holes, using a jig with evenly spaced holes for the bushing to index, having a columns of dowels on either side to center the work.   The 7 hole jig will be clamped at one end of a slat to bore the first 7 holes, then it will slide up to start the next set of holes.  An indexing pin in the first jig hole will seat into the last drilled hole of the last set.  This is repeated until I've gone the length of the slat. That description will make more sense once I get to actually using the jig and I have photos to share.

I started with some scrap MDF to CNC the bushing hole so that the 1" guide bushing would slip in easily but without any play.  After that, I cut a mating plug that would hold the indexing pin (which is just one of the connector nuts that I'll be using to put this thing together).  The plug also needed to slide easily into the jig hole but without any play.

Once I had the sizes right, I cut out the full jig on the CNC.

Ready for use.

I'll use the same guide bushing with two different router bits, one having the proper hole diameters needed for the connector bolt shank and the other for the counterbore.  

Next I can turn my attention to making the slats.