Welcome bud from a Y61 owner :thumbs
Unless someone has done an engine swap in a Y61 or imported one from Aus then the only 4.2 Trols are going to be older Y60s. Rot wise no particular issues that I know of, obviously the younger vehicles are likely to be better and Trols certainly don't have a reputation for having a cheese chassis the way the Discos do but it's the same story as with any used 4x4s, check the chassis/wheel arches etc for rot traps.
Mine is a '54 and apart from the to be expected surface rust on bits of the chassis she's good. Only rot I have found when I've been messing about in the workshop is on the radiator crossmember and I only found that out when I removed the bumper to fit my winch mount. It'll need sorted at some point but is fine for the time being - I stuck some hammerite on it and carried on fitting the winch.
If you're going for a Y61 then based on your budget I think you should be looking at late 2.8s as most of the 3.0s in budget will be early ones and there were a lot of issues with the early 3.0s. Problems were pretty much fixed once they started fitting the 3.0 to the Terranos in 2003 so if you can find a late 03 or younger Y61 in good condition and in budget then go for it.
Power wise the 3.0 beats the 2.8 but neither are exactly speedy as they aint a light vehicle (lwb is around 3t fully loaded). Based on your towing requirements you'll need a manual to stay legal as they're rated to 3.5t whereas the auto's are only rated to 2.5t (but both will pull a lot more if need be).
Your budget will probably throw up a selection of lwb or swb so it depends on your needs as a family car. Lwb is huge
even longer than a Disco 3 and tbh if you're towing near the rated capacity I would be tempted to stick with one of those for stability.
Personally I love my Trol and won't be getting rid of her. She's great offroad, been very reliable and very very comfortable. Just bear in mind parts aren't as easy to get a hold of or as cheap as they are for your Disco but they're by no means impossible and if you really need to you can get parts sent over from Aus (I've only done this once as I replaced and converted the flywheel from DMF to SMF and fitted a HD clutch).
It may not matter to you but for reference the 2.8 is a timing belt so it'll need to be changed at some point. The 3.0 is part timing gear/part timing chain and shouldn't ever need changed as the chain drives very little.
All Y61s are drive by wire throttles.
Both are DMF and, certainly with the 3.0 engine can actually put more power through the flywheel than it can cope with leading to early failure. You can either replace with another DMF or do a SMF conversion like I did. Neither option is particulary cheap but with the SMF it should be a LONG time before anyone needs to go in about there again, particularly if you fit an HD clutch.
Fun fact - The Y61 was sold in Aus with the option of a 4.2 diesel instead of the 2.8 or 3.0. When they produced the 3.0 Y61s they kept the same driveline (gearbox/transfer box/prop etc) but just fitted a DMF :doh instead of the 4.2s SMF. The strength of the driveline compared with the DMF is partly the reason for the DMF failure.
What it means is that if you move a couple engine mounts and fit a manual throttle pedal, you can just slot a 4.2 from a Y60 or Y61 straight into a 3.0 Y61...
Guess what I'm gonna do if and when I have the spare cash :naughty
