k39804 was made in 1981.
The year started at K16266, and ended at K75747.
Your Python is nickel, since Colt didn't introduce stainless until 1983.
To be sure, stainless models have an "S" stamped on the barrel inside the slot for the ejector rod, on the left side of the grip frame, and on the center-rear bushing of the cylinder under the ejector.
Under the grips, the stainless frame is a natural finish stainless, not bright polished even on the Ultimate Stainless bright polish versions.
Typically, nickel guns will have an "N" stamped in key locations, and the area under the grips will be bright and shiny.