I've searched high and low on my axle housing for code numbers to no avail. I need to order new gears for my 12-bolt rear end but do not know the carrier size. The car was originally a 327 powerglide car (67 convert) and the rear end appears to be original (yes I know, odd that 12-bolt posi was fitted into this powertrain). None-the-less, it appears I'll have to open up the diff to find out for sure. What do I need to look for to know for sure what I have so I can order the right stuff? Thanks as always for all the TC help!

Count the teeth on the ring gear and the pinion gear. Divide the number on the ring gear by the pinion gear for the gear ratio, 41/11 = 3.73. If you have a 3.07 to 3.73 then you have a 3 series. If you have a 2.73 then you have a 2 series. If it is a 4.11 then it should be a 4 series, but it could be a 3 series.