The lack of a listing for your floor pan in the Master Parts List does not surprise me, especially if you are looking at the list from a later year.

If there was not sufficient demand Chevy would drop service parts after the vehicle was older. For example, the 1928-1954 Master Parts List does not have the range of service parts for a 1928 vehicle that would have been listed in the 1929 list.

Even the 1940 Master Parts List I have had already dropped some of the 1937 parts.