Will xf Lsd diff fit into Xg ute?

XF Wagon or Ute should. XF sedan wont, but the centre should be able to be swapped.

The XF Ratios are all wrong for the XG though - 2.77 or 2.92 vs (3.23 or so). Will be fairly tall top gear

Nigel

What would that do to speeds and revs would it rev lower at 100 then ?

as above,

But be aware, You may encounter some imperial threads, also XG runs disc rear end.

Either way, it'll fit and be able to be used, but you might have to make up some brake lines, and modify handbrake cables etc.

Also E-series Wagons fit too, but are about 15mm wider.