Create, As a long time owner of Patrols, 2 4.2 GQ's and my current 4.2T GU, I upgraded to the GU from the GQ ONLY because I wanted airbags. The running gear was all identical, what I was tooled up for, and what I was used to driving. I waned to drag my 1.7T caravan around the country with no fuss, so far last couple of years, 2 trips to WA, and one outback trip to Winton, with another in June/July 2011.
I have been very happy with the fuel economy - chase that all the time retired so gotta look after the dollars, havn't HAD to spend a cent on the patrol since I got it, but upgraded the springs, shocks and tyres and exhaust, got a new turbo to put on when I git a round tuit.
For touring, like you seem to be looking at, you couldn't go past it for comfort and reliability. I have found that on some hills with the van it is a bit underpowered, dont know how many times I would have liked a Duramax in it

, but on the other side of the hill you forget about that and enjoy the cold air and the superior ride comfort and great visability and the country we live in.
I paid 28K for a 2000 GU 4.2t four years ago that had been around the continent once already, and thought I got a bargain, so by that measure that value you are looking at is about spot on for the 4.2 considering how rare they are becoming. I remember I paid 30K for my '88 GQ Na 4.2 DX poverty pack with 7K Km's, roof rack, side steps, alum bar, and 7x15 wide rims in 1988 and thought I got a bargain then ( they were 34K new for the DX poverty pack with no extras - Carmichael Ford Townsville prices)
There are plenty of CRD's about and I think that the old grenade days are pretty much gone with the new engines, but I still wouldn't trust them out in the boonies, from a reliability point of view, with my family on board.)
On the other hand my brother in law has a 2003 3l diesel and pulls his 3T plus 28' alum trailer sailer on a steel tri axle trailer, and I was really impressed with how it did the job, and remember thinking at the time, hell the 4.2 would be working its ring out getting this rig going, but I think he's in for a loud suprise down the track. But I wont say "told you so", cause I already have.
The only issue I think honestly bears looking at is the issue of temperature under load, the 4.2t is not real temp tolerant, the cooling system has to be in tip top shape. I know that I have driven the temp guage to the top of the pops numerous times, but about 30 seconds after the load comes off, the temps plummet back to normal, with seemingly no effect, but I know that the effect is cumulative, and a cure needs to be found.
I would think that an A2W intercooler coupled with the head mod cooling rails, cooler thermostat, maybe bigger radiator and a proper digital temp guage ( to do away with percieved overheating shown by a simple hot/cold guage) would be the best solution, but all that is a matter of dollars, not on hand at the moment.
I think that the 4.2 would be the right decision, unless you can get onto a GU with a 6.5 Chev V8 diesel for a reasonable price, they are marketed on the shelf right next to the bottles of rocking-horse chit.
This is just my honest appraisal of a reliable honest workhorse that will last a lifetime if you dont flog it to death.
cheers and good luck with your decision.