GMC AWD Noise

Hello to all,

I have a 96 GMC safari V6, AT, AWD.

The front differential drive shaft (from transfer case) was removed a few
months ago because it was bad,(vibrating at high speeds) and consequently,
it drove fine in 2wd at the time.
Now, above 35 MPH it starts a steady hum in the front end. The pitch
increases with speed and it seems to level out at cruising speed on the
highway.

I have pulled the front diff in an effort to find the problem. Luckily, I
must say that the diff it was real easy to pull.
It seemed that the backlash on one side was a bit excessive -( I don't know
the Specs) and it seems on one side the gears may be rough like they are
catching a bit on the edge of teeth.
Will this be hard to rebuild? I have never rebuilt a diff or AT before;
gearboxes/engines/diesels yes.
Based on description would diff be at fault?? CV's and bearings seem okay,
no play at all.
So now I need info and advice, I can't ID the differential, no tag and the
stamped numbers don't match anything.
Any help appreciated.
Thanks,
tink