Id put the 300tdi in it simple conversion looking around on ebay i rekon you could do it for less than 1500 quid.
That's if your lucky, and whether you do 'an as factory' install.
It's all the smaller bits and pieces that can put the cost up.
To do a factory install you need:
The Engine (complete)
The Gearbox
The Exhaust
Front and Rear Propshafts
Correct Radiator and Intercooler (and all the pipe work)
The Air Filter Assembley and pipework
The Fuel Filter housing and pipework
The Oil Cooler Pipes
The Bonnet Stay (an non Tdi one is different)
The correct PAS bottle and pipework
Engine Loom (and the heater plug wiring)
The Fan Cowel and Fan
Both driver and passenger Flooring
The Transmission Cover
And the seatbox or the correct adaptor (as the transmission cover is a different shape) - so you'll also need the correct floor mats
Ideally the correct header tank
The correct chassis/gearbox crossmember
And a few other bits and pieces.
You could cut this list down by mounting the engine and gearbox slightly further back than a standard 300Tdi Defender - this means the gearbox would mount on the same mounts as the LT77 - but then this also causes problems - namely the exhaust and the oil cooler pipes won't fit.
Ian