Early Model A Houdaille dampers used glyserin. Many of the model A suppliers carry an oil they list as shock oil. Since the shock action and performance depends on the viscosity of the fluid used, the replacement oils were likely developed to get a viscosity that will work over a wide range of temperatures. Most folks keep there cars out of the rough weather so the temperature won't be as big an influence as it was back when you had to depend on these cars for daily use.
I'd just buy the stuff that Bratton's, Snyder's, Mike's, or on of the other Model A vendors sell. The other option would be a recommendation from a rebuilder of shocks if they have a different opinion.
Kerby