Wow, that place is still in business? I ate there for the first time in the early 1980s. I don't live in CA any longer, just saw the name pop up on the recent posts list when I logged in. Anyway carry on.
Google Dr. Hogly Wogly's macaroni salad recipe. There are several blogs giving the recipe - not sure how close the taste is, but it sounds pretty simple. Could be the brand of mayo that's important.