The preview and dedication day was held on Sunday, July 17, 1955, and televised nationwide by ABC TV, a major investor in the project. The official grand opening was on Monday, the 18th.
In the center foreground, is what appears to be a radio truck with a generator on a trailer behind it, apparently used by Disney personal or a subcontractor for communications. The rest of the lot is filled with 1940s to 1950s cars and trucks and a few from the pre-war era.
My mother, sister and I went there about a month later. I was eleven at the time and what a wonderful day it was.