With all this wisdom out there, i'm sure someone can help me with a question.....65 Plymouth Fury III, 2Dr, HT....

How do i tell what rear end i have?...it's a rebuilt 1972 318 w/ 727 trans

 

It should have a 8 3/4 rear end. If it is original it may have a metal tab under one of the bolts with the gear ratio. Stock it probably had a 2.91 gear

 

Other comon ratios are 2.76 and 3.23.

 

to find out the ratio, wedge something in front of the front tire, put the car in neutral, jack the car up until the back tires are off the ground

make a chalk mark on the driveshaft, and a chalk mark on the tire
give the tire one complete turn and count how many revolutions the driveshaft made
that is your ratio