You can use a T6060, if you want to fit a Magnum gear set then you can pretty much choose your gear ratios but it very expensive, the T6060 is a much better box than the T56 far better and smoother gear changes.
But as Rod says the ratios are much better suited to a big torquey V8, for the money it would cost you to get it right a Tremec TKO600 would be a better bet, I believe that's what Rod has fitted to his Sapp.
Also would be worth speaking to Gav Diamond on here as he has also done the TKO600 conversion on his 3 Door.
Rich