It's a good idea, but it may not be quite accurate enough at just 1 turn.
R151F (Turbo 4cyl) have a 4.31:1 First Gear
R150F (V6) have a 3.83:1 First Gear
G/W-series have a 3.95:1 First Gear
L-series have a 3.93:1 First Gear
So you are comparing a 4.31:1 to about a 4:1. In this case I would mark the shafts again and turn it maybe 3 times. Then you would compare about a 13:1 if its a Turbo or it would be about 11 3/4 if its not.
And if its a top shifter t/case then oh-boy
Turbo:
vs.
W56-B:
