but it can be very hard to find ANY picture of the side streets

This picture is circa 1950, the Ace Bar at 111 S. First Street. (Ace Bar 1945-1951)

From c.1939 thru September of 1945, Al's Bar (Mgr. Al Salton) was at that address. (Don't really know when it opened, but it's in the 1939 phone book. It's also in a Sept. 1945 business directory...but by the Nov. 1945 phone book Ace Bar is at that address)
Here's a swizzle stick from Al's Bar ("See Boulder Dam at AL'S BAR 111 So. First St. Las Vegas, Nevada")