-----------------------------------
I had the rear end cover off. I could not count all of the gears of course but I estimated 66 on the big spline and about 16-18 on the smaller. What kind of gears are these? Is a 12 bolt the right rear end on a 72 Chevelle. Thanks in advance!

you divide the ring gear tooth count by the pinion tooth count...

66 / 17 = 3.88 gears

you probably have 3.73's or so..

Mike