Hi Rizhto, Both are correct. The early 1927 and 1926 Landaus were taller 7 window sedans. The later 1927 and 1928 were lower 5 window sedans and called "Imperial Landau". I can email ads for both but I don't know how to upload the photos here. If you look in your 4-cyl parts book, it will list both.
For a short time in 1929, the landau bars were real and the back of the sedan roof folded to let the rain in.
In the mid 1930s, Chevy taxis and limousines were called "Imperial Sedans" in Europe. There were two jump seats
to effect the 7 passenger status. Here's a web page: <
http://home.znet.com/p1937/Limo.htm> . If you look in your 6-cyl (USA) parts book you will see it listed as a 1938 taxi. Some were badge engineered as Yellows or GMCs in USA.