I'm adding some 3/8" steel dowel pins to my fixture, along with four hold-down bolts. Below I'm reaming the clamp plate (which will have clearance for the 3/8" pins) but the base will have press fit pins. The 3/8" hole in the center is a tooling hole that also lines up with one of the same size and location in the base. This way I can make sure that everything lines up when I'm finished.
 

Here you can see the steel dowel pins along with four springs. The springs will help lift the clamp plate once I loosen the four bolts making it easy and convenient to slide my work piece.
 

I'll be using a Nut Driver to tighten and loosen the 1/4" bolts. This method should work great compared to a ratchet and socket because the bolts don't need to be "that" tight. Now it's time to cutout the profile of the slot that I want to produce on my work pieces.
 

Below you can see the shape that I'll be cutting out which is in pencil. I'm going to rough-out the hole first using a 1 3/8" Forstner bit.
 

Next I used my boring head to produce a 1.500" diameter hole. Could I have used a 1 1/2" Forstner bit for this? Yes I could. But I wanted a nice finish so my flush-trim router bearing would ride on a nice smooth surface compared to a rough one. Is this overkill? Yes it is. But the results should justify the extra time involved.
 

I wanted the slot portion of the cutout to be nice and clean without any tear-out (arrow). To make sure the edge stayed nice and sharp, I cut the slot using this scrap piece in place. This way when I cut the my shelf pieces, those edges will be nice and clean as well.
 

This slot is 1.500" wide, which is what I need so the bottles fit the shelves correctly. But as you can tell this slot goes into rail by about an inch. This is so I can drop the router bit into this area before starting my cut. In other words, it gives me a place to start, go around the U shaped slot and then end in this area.

Also notice the new smaller slot at the bottom. This is going to be my "viewing window" to lineup my work pieces with. Notice the pencil line, it's on the same center of the U shaped cutout. My plan is to put a line on all my shelves, line up both lines, and then tighten down the clamp plate.