Grenade replacement

You would have to fit the gearbox and transfercase as well. And probably re engineer the front end.......Big job!!!

It'll go straight in, some bits and pieces may need to be changed, i'd guess the bellhousing may be different, but considering they run the same gearbox (assuming the zd30 is a manual) you could just use the bellhousing from the GQ - if the zd30 is auto then just swap out the GQ manual box along with the motor.
Engine mounts shouldn't be an issue as the GQ and GU run the same chassis - so you should just be able to pilfer gq bits if required.
One of the big things would be tidying up the electronics as the TD42 is not an electronic motor - you may get the dash telling you theres fault codes etc when you arent running an airflow meter, electronic controlled pump etc, tacho may need some thought to make it work ok (one way would be to get the instruments out of a 4.2 GU)
All in there shouldn't be much custom work involved as the GU came out with the same motor you're looking at putting in, so if there are any parts that you require and cant pilfer off the GQ then you can get them from nissan or maybe a wrecker.
You also shouldn't have to worry about engineering as the td42 came out standard in that vehicle - and has less power than a zd30.
Cant think of anything else right now, but considering GQ and GU run the same chassis, diffs (with exception of width), suspension gearbox and most mechanicals.
There shouldn't be too much in it.
Really the main difference is a new body and the adoption of the ZD30. (rd28t, tb42, td42 were commont ot both models)

Like Willem said, BIG job replacing it with GQ motor (definately need GQ g/box too). Try getting a 4.2 donor motor from the GU, I believe a Qld member called Grungle has done this to his 2.8 GU, if I remember right it cost him about 10G. Drop him a line and get all the low down.

Cheers, Trevor.

Ok then, a td42 GQ should have a plate in the engine bay on the drivers side, on this plate theres things like engine model/size, paint colour, and manufacture plant.
There should be trans,axle and next to it there will be FS5R50A HG41 or something similar - thats off a 1993 GQ TD42
What thats saying is the gearbox model first (FS5R50A) and the diffs second (HG41) meaning a 4.1:1 diff ratio.

Check your GQ i'd say it will say the same, make a note of the numbers.

There should be a similar plate on the GU on the firewall somewhere, that will confirm or deny our ideas about whether the gearboxes are the same or different and if the diff ratios are the same. (or you could just give the box a visual check)

I'm pretty sure thought that the ZD30 runs the larger box...

A drama with convering an rd28t to a td42 (like was posted above by a member) is that apart from having a smaller gearbox the rd28t usually had 4.6:1 (HG46) diff ratios - fine if you want large rubber - not so fine for touring with a td42!

Do a search for "Project TONI"