Personally I really love diesels

espcially for off roading, but in the US it seems like a lot of hard work IMO.
With the prices you guys pay for petrol (gas) I'd probably stick with a V8. And yes I know you guys often complain about gas prices, but consider we in the UK still run V8's and pay 95p litre for regular unleaded.
My choice would be a stock Chevy Ls1 V8. I'd choose this engine for several reasons:
1. It's fairly small & compact
2. Easily fits in the engine bay
3. Is aluminium and fairly lightweight
4. Pretty cheap and very available in the US
5.Very powerful (320-350bhp and 350-370lb ft,
over 95% of torque from 1500rpm!!! )
6. Conversion kits exist for Chevy SBC swaps
7. More economical than a Rover V8
In years past big GM diesel V8's have been popular swaps in to Land Rovers here in the UK, but they are generall big, heavy, uneconomical and not all that powerful.
Fitting any other diesel in is possible just make sure you do your R&D first. And as much as I love the Tdi's units, I probably wouldn't advise one for use in the US unless you have special reason to want to.
Do you guys get Ford Transit vans in the US???
The diesel engine (2.4 DOHC 16v) from them will be finding it's way into the new Defender, available in a month or two in the UK. This may be a possible route to go and being an OHC common rail diesel I would think it will be very tunable and offer more HP than any of the other Land Rover diesels (Tdi, TD5).