1973 340, want more power.

open diff= 2 rotation of tire and count driveline turns. suregrip, both tires need to be of the ground, turn tire "1" turn and count how many turn the drive line turns.
2.76 =2 and 3/4 of a turn on the drive shaft. 3.55- 3 and 1/2 turn of the drive shaft.
simple and you will know without pulling it!