[GPierce]

MikeV in Florida posted this in 2016. It worked easily for me.
Quote:
Lots of things can change in 80 plus years. Jacking one rear wheel up and turning the engine over by hand will let you determine the ratio. Easiest to pull your plugs and get your hand crank out,
Put it in 3rd Gear.
Make a mark on the jacked up tire at 12 o'clock and crank the engine over exactly 2 revolutions. When you hit exactly two revolutions, have a friend grab hold of the tire so it cannot move, or set the hand brake or whatever.

See where the mark on tire ends up:

Between 11 and 12 o'clock, ratio is 4.11
Between 12 and 1 o'clock, ratio is 3.78
Between 1 and 2 o'clock, ratio is 3.54
Here is the info I have;
Jack up one rear wheel.
Pull your plugs and get your hand crank out,
Put it in 3rd Gear.
Make a mark on the jacked up tire at 12 o'clock and crank the engine over exactly 2 revolutions. When you hit exactly two revolutions, have a friend grab hold of the tire so it cannot move, or set the hand brake or whatever.

See where the mark on tire ends up:

Between 11 and 12 o'clock, ratio is 4.11
Between 12 and 1 o'clock, ratio is 3.78
Between 1 and 2 o'clock, ratio is 3.54

These are from notes of the procedure that I have taken from another Barner's post.