8 3/4

'71 Would be a 4" bolt circle originally. Yes it could easily be made into a posi, either by installing a posi type differential in your exsisting center section, or by replacing the center section with a posi equipped unit aka "chunk". If you want to verify the gear ratio w/o taking it apart you can turn the axle 1 complete turn & count the # of times the yoke turns & that will give you an idea. For example, if you tuned the axle 1 complete turn & the pinion yoke turned about 3-1/4 turns you would have the 3.23 gears in it.