I was thinking about right angle adapters, too, but those create a whole separate problem with wiring (namely conflicts with adjacent connections).

This may be the engineer in me pushing against aesthetics, but I am a big proponent of having decent access to the back of my gear. It makes ventilation better, it reduces headaches during setup, it leads to fewer mis-connections and loose connections, and it tends to make for tidier wiring.

How will you access the units to make the connections? Will they have to slide out (meaning you need 18" of slack to allow the equipment to come forward while remaining connected), or do you have a way of connecting the gear once it's on the shelf?