The Brown Derby location used in the “L.A. at Last” episode was located at 1628 Vine Street in Hollywood, just below Hollywood Blvd. Sadly, in 1987 this historic restaurant was lost in a fire. The Taft Building and a  facade of the nearby Dinner Bell cafe remains, which has been part of the Hollywood revitalization since the 1990’s.

Here is the screen grab of the  ‘watering hole’ where Lucy, Fred and Ethel meet William Holden and  below a fun, vintage postcard of the actual location with arrow indicating the approximate colors of the same sign with the yellow neon of “The Brown Derby” and the white neon of “Restaurant”.

1950’s color footage of The Hollywood Brown Derby near the start of this video.
And  the same location as it is today…

A comparison of a 1940 photo with a current picture shows the Taft building with its fire escape on the left and a facade that corresponds to the Dinner Bell Cafe ( the old street no. of the Dinner Bell Cafe was 1604-1/2 North Vine Street). The  Brown Derby location seen on the right of the old photo has been taken over by newer  buildings.

The Hollywood Brown Derby features in the the video Game L.A. Noire see walkthrough on Youtube here

Reference:

• Dinner Bell Cafe “On October 7, 1939, Deputy Swift stumbled his way into The Dinner Bell Cafe at 1604-1/2 North Vine Street, adjacent to the Brown Derby in Hollywood.” http://derangedlacrimes.com/?p=4297
• http://www.ign.com/blogs/vampirehorde2/2011/07/07/l-a-noire-hollywoodland-tour-guide-now-and-then