Identify a rear end

I have an axle/differential marked GM79 on one axle and the numbers 3896839 on the other axle. It appears to be possitrac with a ratio of about 3 and a quarter( a little less).The wheel pattern is 6 lug. I'm trying to figure out what this may fit.Year? Truck? Whatever I can. Anyone have any idea where to look (or know themselves)?

Do you know if it's a 12 bolt or 10 cover. It bing a 6 bolt most likey out of a 3/4 4x4 has to see if I can find some more info.

12 bolt cover. Any ideas with that?

pretty sure it 1979 three should be a code on the diff that will tell you the diff size or get the # off the in side gears. pretty sure the 3896839 code is the GM diff housing cassting #. I have a few but can't come up with that one.


It's a little hard to see the #'s on the ring gear but you can make them out this is a open 3.42 diff . There should be a 3 code can be two letter one number or one letter two numbers. if you can see them still.

this will give you a idea where and what what #'s

Thank You very much Pontiac1976. I will let you know if I find the numbers. This is a huge help. Your picture is exactly what is in my shed (looks) . Fred