Rear 12 bolt diff with GM 78 stamped on it ?

[454 blazer]

Hey guys,
quik question regarding a rear diff i got of a 78 blazer , it has GM 78 stamped on one side and a number on the other (3896839 N ) does this mean anything or is it just a bog standard dif , the one i am running at present just says GM 12 .Is there any difference between them ? do these numbers mean anything ??Any help from you legends would be appreciated .

 

[454 blazer]

Nobody ?

 

[imiceman44]

Nobody ?

The GM 78 doesn't mean much
The other number is a serial number.
Can't remember if you can decode it but the best thing to is find out what ratio it is.
You could open it but if you didn't buy it yet and want find out roughly what the ratio is, you can count how many revolutions of the yoke to make a full turn of the wheel:
If you do this with an open diff, your number will be half of the ratio, unless it's a limited slip and both wheels turn together.