It is always advisable to have the van level, but you need to do your measurements with the van attached to the car. It may drop more than the 50mm if the tow ball down weight is too much and thereby the back of the vehicle drops.
After checking the level of the van, sometimes you can invert the tow tongue and thereby raise the two ball - but that may be too high!

Although I have a fifth wheeler so I'm no expert on conventional vans but , I would be trying to put the van tow ball weight in the back of the tug and then aim to have the tow all height at the same height as the van be this achieved by lifting the tow ball by turning it up the other way as suggested or by fitting better springs if they are not up to the task allowing for the van level to go down a bit when loaded.
Woody

Load car and van to travelling weights.
Balance loads to have each veh level at start.
Back up to van
Then adjust Car tow hitch height to suit.

H.R hitch adjustable vertically. Tongues have assorted drop heights .

As long as you don't have a 4wd and little road pop top van.
OR visa Vera.
You shouldn't have too much problems.

Don't try to match a severely mismatched pair.
You'll have nothing but heartache down the road.

With that rig though a 2 in drop, tongue. Should be fine.

If your tongue new.
Either go to where purchased or another tow bar dealer,
They normally straight swap. or maybe a little extra.

You live near Yeppoon I'll give you one.

Thank you to everyone for your replies, have been busy the last week with family matters so will be back setting things up next week. Still trying to get away for our first weekend and still have the lawn to mow. Wonder which will be done first. Cheers

-- Edited by CC Bear on Sunday 14th of August 2016 02:40:21 PM