[mylesdw]

I think the Jag IRS will take your 450hp ok, the Salisbury diff is quite strong but its weakness is in twisting of the lower wishbones under fierce acceleration so if drag racing is more your thing than track it may be better to stay with the live set-up.

The fitting of radius rods to the Jag IRS is a very contentious subject. Put simply, if the chassis pivot point of the radius rod is not on the projected inner pivot of the lower wishbone, the radius rod does more harm than good (assuming the diff is solid mounted)