Right, but to really clarify Mustangs are really solid axle 8.8s so a IRS 8.8 diff is needed, meaning Cobra or as I used and as far as I know the same as Cobra, MarkVIII diff.
With good fab skills between me and ILLS, and his good welding skills, I remember being $1500 in or so. Without the skills or means to do the needed fabbing.....cost is hard to say. Finding someone to take it at a shop on with little more than posts on here about mine that it works well will be hard.
Having the only 4.10ed LS around.......priceless.
As far as I know anyway.