12 bolt rear end question

[maxreps]

Mine has richmond 4.10's and an Eaton posi unit in it but I want to swap gears and go to a 3.08-3.2X(future700R4 hopes). I will have to get an entirely new Eaton unit won't I, since they have one for 4 series gears and one for 3 series gears?

That really stinks if I do because the Eaton is very nice and basically new too. It was put in with the gears about 6 months ago, by the prev owner. Maybe I could sell/trade one or both items or something.