I think it says in the haynes, and certainly can be found searching on here- you need to check what age the gearbox is to determine how you get it full. Earlier ones have a lower filler hole, and need a dose of oil down the speedo cable, newer ones have a higher hole, so just need filled to that....
Anyway, in response to your question, Jack it at the front to drain the oil, no probs there. I think I finished refilling with passenger front wheel off, and a jack at that corner and I just lowered the jack till the car was sitting about level. If your gearbox oil bottle has a spout on it, you'll have no bother filling up to the hole like that. Once the oil is level with the filler hole your done (if its a late model box).
Alternatively, late box solution again, jack the passenger side higher when filling, over fill with oil, then leave the cap off the filler plug and sit the car down level to drain off the excess. Jack on passenger side and refit plug.
The side to side level-ness is way more important than the front rear levelness, i think, as the filler hole is on the side...
HTH, and makes some sense!
