the normal rwd ratio's are 3.92:1 or 3.64:1
the 4wd cars use a 3.92:1 on the dohc cars only, be they badged xr or ghia
the rest of the range used a 3.62:1 diff front and rear
BUT
even though the 2.8 sierra's used the same ratio's, you cannot retro fit the 2.8 front diff onto the other 3 sorts of sumps (2.0 twinky, 2.0 cossy or 2.9 12V V6) because it's different and don't fit, even though some peole will tell you that it does