Axle identification

Need to change the backing plates and axle seals on my 2004 Yukon.

They list 8.5", 8.625" and 9.5" rear gears.

I know it is a 3.73 Positrac rear. (Codes GT4, G65, G80)

Nothing tells me what size the gear is. Any help on which seals I need?

Thanks.