Just pulled the shocks off my '49 3100 and to me they are single action. I mounted one in a vise with the arm horizontal as it would be installed. I have resistance pushing down but they spring back to horizontal without any work on my part.
One had a lot of resistance and one was much weaker which makes me think that it needs fluid. The body also showed signs of fluid having been on there at one time.

1949 Chevy 1/2-Ton
"Sedgewick"
In the Gallery
1989 Caprice