[Xlot]

G28/10 is from an 85/86 Euro - according to the 928 Specialists website.

Its most likely 2.73 final drive ratio.

You can swap the diff to add an LSD, but you need to move the crown gear over from the open diff to the LSD, as the crown and pinion are a matched pair.

Not a tricky job - just have to work out the shims to set backlash correctly (measure the original open-diff backlash reading before disassembly, so you know how much wear there is beyond the spec etched on the side of the crown wheel, and aim for that as the "new" spec when shimming backlash with the LSD).