That Walthers kit #933-3076 was in their 2000 catalog. It included two of the unloading ramps. Each ramp measured 9.5" long x 1 3/8" wide. The kit also included a corrugated metal office building measuring 2 15/16" x 4 1/16", a chain link fence, and a guard shack with gates. It looks like the guard shack was 1 1/4" square, but it appears to sit on a 3 11/16" long x 1 1/4" wide concrete island. Also included in the kit were two auto carrier trailers. Available separately was the matching "Auto Carrier Semi" truck (Ford LNT 9000 tractor) with trailer was #933-1200.
Good luck in your quest.
The kit was part of their "Driving Force" series of kits that included several structures relating to the manufacture and distribution of new American cars (some based on structures used by Ford Motor Company).