So now that is (almost) complete, I've got to figure out how to support this. Many moons ago, I scavaged this and have had it kicking about since. It is a rack for a Motorola CentraCom I - A Police Dispatch Console:
Cleaned it up, filled some of the deeper scratches with glazing putty and gave it a few coats of Rustoelum "Deep Canyon Black" paint:
Most rack mount stuff is just bolted to the front but this thing has got to weigh 180 pounds. These mystery parts were supplied to support the back of the rails (very poor assembly instructions):
Here are a couple views of the rails.
As you can see, the sliders fit extremely close together.
The far end already has its own ears
Although it appears they actually intend you to attach these as further extension to the rails, I inverted them to reach in towards the rack. One of my techs gave me a hand and we slightly modified a pair of rack extenders (intended for a Motorola MTR2000) for them to mount to. It worked out well and is very sturdy. With the computer mounted flat to the rails it is stable. However, if it is extended beyond 14 inches or so it starts to get tippy - definitely a two man job at that point.