Dean,
what gearbox is it exactly G96 /90; G96/50, G97/90,
Usually not much is needed for flip those, as Cliff said. I usually like to add a thread into the diffhousing for a tempswitch.
You would have to flip the vent and drain plugs.
Also a take of and return bung for an oil cooler setup would be great. If it is a box with the oil upm already integrated than you would need to adapt the pick up tube to thenew orientation . I would not dare to change the spray tubes, because i think it makes not if a big of an difference if the gears would be sprayed from the top or flushed from below.
Other than that make sure you fill in enough good oil. I´m using SWEPCO 210 and fill at least 5 liter into the box. if it does not spill any of the oil out i fill it even more.
TOM