The 5.83's don't exist as far as I am aware.
They had fronts... or rears... or something and always said they were "waiting on more from the supplier" but the supplier, richmond gear, had never received an order from Calmini.
Sorry, you're stuck.
31's are OK, but a bit marginal on road. You won't use 5th all that much any more.
Offroad it will be pretty bad. Transfer gears will totally fix the off road behaviour, but not on road.
There is the undertaker:
http://www.trailtough.com/index.php?pag ... &Itemid=53
But that's a pretty expensive solution for 31's.
Steve.