If you Google the model of your Even Brake, you'll find a lot of documentation from Roadmaster about their various brake models. Yes, you've listed the parts that usually come with the system.
To test the box you have, sit it on the passenger side floor, plug it in, and take a drive around the block. Braking at various rates should make the brake pedal lever activate, so you can try different sensitivity settings. If it doesn't work at all, you'll have to decide if it can be repaired and whether to invest in the missing parts.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI