On what to look for, main things are rust like with most 4x4s.
Y61 Trols are notorious for rusting at the radiator crossmember "the factory rust".
Apart from that, if you're looking at 3.0s I would try to stay clear of any 3.0 older than late 2003 when Nissan refined them - a lot of the early 3.0 engines were trash. Some of them are fine but it was the early ones established a bad rep for the 3.0 which has been hard for it to shift.
Later ones should be no bother as long as you keep them serviced. I had my 54 plate for 4 years, 3 of them as a daily, and she was modded and used and abused offroad throughout that time (and as far as I know is still going strong). I only sold her as I wanted a 4.2 and the right shorty came up at the right time.
I did some engine mods but if I was going to press you to do any of them I'd say fit a catch can. You can do others but I'd say catch can is the best if you have to pick one.
The number one rule with the 3.0 is that you need to do a bit of research before doing most engine mods as it's ECU controlled with various sensors and changing one factor can have an unwanted knock on affect.
Blanking the EGR is a classic example as if you don't adjust the turbo boost when you do it, you can cause the engine to start overboosting which then leads to bang time.
I blanked the EGR and had a straight through exhaust after the cat on my Y61 but I also lowered the spool rate to compensate and had no issues (I quite liked how the combination changed the characteristics).
Hope that's some help :thumb2
