Hi..does anyone know what it takes to make a 4wd rear diff fit on a 2wd car ??

 

You'll need a std sierra rear beam to fit a 7 inch 4x4 diff.
The 2wd diff is 7.5 so the baem is different, but all other sierras used 7 oinch diffs iirc

 

Ok...I take that the 4wd diff is somehow smaller.... do you know if its possible to mount it with spacers, as it is only to make a tests, as there is a "noice" when driving, and it appered after I put on a fresh rebuild gearbox and rear diff ..... ?

 

I would imagine so, might be worth a try to see if it fits