Speedometer Gear

I need a new Speedometer Gear for a 1965 SF, 383, 727. There is a multitude of different gearings which seems to be color coded which in my case is green. There are three different gearings for green which are 31, 34 and 39. However, I readily can’t physically get to mine do does anyone know what the gearing would be? Thanks.
Author: Mudeblue