ok - as you've already figured out I see, if convicted you WILL lose your licence for 6 months. (not more, no less). You'll also get a fine + court costs somewhere in the region of $600-700 total.
Options are:
1) Plead guilty. You will have a 15 min meeting with a duty solicitor on the day, prior to your appearance. He will first check if the police have filed the charges correctly - it's been known to happen that they haven't, if thats the case you are free to go
. Realistically slim chance of that. If you drove to court on the day, the DS will also request the judge to start your 6 month suspension from midnight that day, so that you can still legally drive home.
The outcome of this - you walk away with a smaller fine + it's easier and cheaper to get a work license should you decide to get one.
2) Plead not guilty. the judge will then schedule another hearing for a later date (usually 1-2 months). Upside is you can still legally drive during this time (once the intial 28-day suspension finishes) and you have time to get a decent/cheap lawyer to represent you and get a limited license if you lose.
Downside is if you get found guilty anyway they will impose a bigger fine. There's a possibility of your lawyer arranging a deal with the police prosecutor where you plead guilty to careless driving rather than dangerous = 3 months license loss instead of 6.
Being in CHCH I would say chance is against you.
There have been cases (2 that I know of) where people had the charge dismissed after showing data logs from engine management computers (showing they never exceeded XXXX rpm, or a certain speed) but not an option for you seeing as presumably you dont have such a device in an old van.
If you are going to fight it prepare to cough up around $6000 for legal fees + another $2000 for a work licence should you lose.
The cost that different lawyers charge to arrange a work license varies MASSIVELY from 1 lawyer to another, so shop around.
The cheapest option is to plead guilty and drive carefully and sedately for the next 6 months (shouldn't be a problem in a Hiace
) and don't do burnouts in stupid places...or anywhere at all for that matter.