Some good stuff coming in on this thread.
A correction. The Motorola key you need is a 2135. It locks the handle used to release the radio chassis from it's mounting plate.
The DEK connects to the control head VIP port via a cable. You can have a max of three DEK units. To connect, for example, two DEKs, DEK 1 cable would go to the control head, DEK 2 cable would plug into DEK 1. This is a daisy chain.
Your switchbox for lights does not connect to the radio. It is just a nice set of switches that can control other equipment in a systems 9000 enclosure so it all looks nice. They are not heavy duty switches so you cannot run a 30 amp lightbar through them. It's intended purpose is to run other relays to handle the big loads or inputs to a smart lighting controller. Wouldn't run more than an amp through them. Good news is, see attachment for a rare document on this.
As far as sprucing up the heads, armour all is OK, a plastic restorer is even better. Do not use an ammonia based cleaner (409) on them. It will remove the logo type and give the plastic a whitish haze. Use a mild detergent or simple green and water with an old toothbrush. If you want to replace the housings, they are probably available still, although the control head may say "Astro"