Hi Mitch,
Welcome to Expo. Heaps of info in the threads on single rear wheel conversions. "SRW". You can go back a fair way and we've been talking about it a bit of late. I know I posted a few pics of all sorts of different tyres standing up together so you could get an idea of what they looked like compared to one another.
Basically if you derate your truck the problem is'nt so much the tyre selection as it is the wheels that are available. You can actually get away with standard rims and Michelin XZL's but the price of these has shot right up over recent times. Used to be $500 each. Now with a tube they're nearly $800 each and that's if you qualify for a good discount. Also supply is reall sketchy. No mistake , they are an awesome tyre but only expect between 50 and 60 oooks from a set on your FG.
About rims If you go with standard rims , they only have very thin centres. I know you are going to derate your truck but you can bet if it's a crewcab with a tray and all the gear loaded up you will be every bit of that GVM. The centres of the wheels will eventually let you down. They crack between centres. One truck here has started to crack centres at 6 months old.
Solution to that is going to 19.5 inch wheels. Super strong but you are limited in tyre selection. We've been running tubeless Toyo M608Z's now which seem to be the best option so far. Really tough looking Mud+Snow pattern. A bit over $600 each but they should give a lot more K's than the XZL's for general on/offroad use. The previous best was the Hankook AM02 at a bit over $500 each depending on where you shop. Where are you exactly? I'm sure Portheadland or any of the big mining towns up there would would carry these or certainly be able to get them in quickly.
One thing we're finding with the Toyo's is they won't air down and belly out as much as say the XZL will, but with the extra power of the new FG84 they seem to perform just as well if not better than the older FG649 with less power but XZL's aired down for soft sand. This is because they have a really strong sidewall but maybe that's a good problem to have. I know all the beach operators were initially worried but seem to be relieved at not having to replace cracked rims again.
Just make sure if you are buying wheels for your truck that you state that it's a new model because they have 6 stud wheels. All the early Canters are 5 stud. As some of the Americans are starting to find out , you won't regret going to single rear wheels and expect improved performance and economy from the higher gearing. Gearing seems far more correct with wheels around 900mm high than 750's.
Sorry for sounding like a salesman but SRW is probably one of the best mods you could do to your truck and in the long run will probably pay for it self. A couple of other little things you have to do to make it all 100% legal too.
Regards John. Hey post some pics of your truck. The Americans don't get them and I don't think any other of the Aussies have one either. Very cool.