Hi,
My suggestion is to put a water filter on the coolant system. I have mine installed on the heater hose line, and it will clog with debris each summer, and I replace it in September. It keeps the cooling system clean, with no buildup of minerals on the radiator. Water coolant filter is Napa part #FIL 4070 and the kit to install it on a 5/8" heater hose line is FIL 4019. I found them at the local Napa store on the shelf. I put mine just behind the bumper on my motorhome, so I can put a 5 gallon bucket below it while changing the filter, I put locking pliers on my heater hoses (with rags to protect them) to keep most of the coolant in the system while changing the filter - it only tanks a couple of minutes.
My other suggestion is check the weight of the van. If you are going to install 4 wheel drive, it should add around 400 - 500 pounds to the already heavy front axle. I have heard that professional conversions of ambulances cost about $25,000 when they where new. So now most ambulances that are 4 wheel drive are using the less expensive F-450 chassis, even though it is slightly longer than the E-350/450 van based ambulances.
You most likely would do well to install the heaviest van front springs that will come with that vehicle. If you can add a extra inch of spring height, then you will have a bit more ground clearance.
Is it common to buy 16" tires in Australia? Is it more common to buy 17.5" tires or 19.5" tires? You might consider changing to a common size in your home country before leaving the US. You might get another inch of ground clearance by going with a slightly taller tire.
The rear axle is rated at about 7,500 pounds, but is limited to only 6,000 due to the tires (and rims) being rated at 3,042 pounds each. Only the trucks got heavier rated rims and tires in 2005.
Is it your plan to get a axle from a junkyard F-350 or F-250 4 wheel drive and convert the van with those parts? By using F-250 and F-350 parts, you can also change the rear axle too, and then use the heavier 17 and 18" rims that came with those trucks, and the 3,200 and 3,400 pound tires used on the 17 and 18" rims. They have different bolt patterns than the E-series vans.
I think that the F-250 has independent front axle, while I hear the F-350 has a solid front axle. If you find one with 4.10:1 rear axle ratio, you probably can go with larger diameter tires without reaching to low of a engine RPM at a given road speed. I would not want a lower rear axle ratio than 4.10 because the diesel will get better mileage while turning a slow RPM at 65 MPH. If you do not plan on using taller tires than stock, then the 3.73 will work fine, and might be more common in a junkyard. The engine has plenty of power to move it's weight around, especially compared to the low powered Australia vehicles.
You might also consider a larger fuel tank here in the US, as importing one might be more difficult, and they are not regular production items in Australia. Transferflow.com is one great place to get them.
Fred.
