It is an interesting question under slinging.
I did to my first van in 2011 .... easy to do but the rules
http://www.comlaw.gov.au/Details/F2007C00494
have a look at this first
http://www.infrastructure.gov.au/roads/vehicle_regulation/bulletin/vsb1/vsb_01_b.aspx#16
If you have an overlay axle flipping it is not an option due to they often have a bend in them making the camber ?wrong.so the guide tabs have to be relocated and the spring assembly bolts reversed, a strait axle is easier. Should be around $400.
Now that your head is spinning Take a look at a new boat trailer and some Aussie built big vans and you will find ball heights well outside the rules and even tail light way too high so you can make up you own mind .I just mention this cause someone else will.
Try ring the RTA and ask for an engineer if in NSW ,I was pleasantly surprised. The 3 insurance companies I rang just wanted it to be done in a professional manner(not necessary to be a professional). And don't forget to add mud flaps.
Raising our expanda made it a lot safer to tow as it no longer bottomed out in pot holes or driveways.
Check current regulations for your state ,I heard a mod sheet has to be done now?
The other bonus items , I found fish plate cracked Guides out by 17 mill on one side of the axle leading to bent hangers and skewed axle ,bolt locking weld failed so spring bush badly worn(van had less than 8,000k on it. And very poor welding even mine was much better!
Have fun