am building a 110 with a 300 tdi / R380 and my donor vehicle is a standard diesel. I have been told that I may need a different tunnel and bell housing. Is this true?
Depends....
If you want to fit the 300Tdi in the correct factory position...
then yes... you need the correct plastic/fibre transmission cover, the correct bulkhead to transmission tunnel section and either a 300Tdi or Td5 seatbox (or AFAIK you can get a panel to adapt your existing seatbox)
Or....
If your not bothered about 'as factory' spec...
You can mount your R380 off the the LT77 gearbox chassis mounts (just need to swap the mounts off your existing box to the R380)... which will put the gearbox 2" further back than standard for a R380 - but in the same place as the LT77. Which means all the floor and transmission covers will stay the same, as will front and rear props...
You then need to fit engine mounts to suit (this has been covered before one here) - which will mean you engine sits 2" further back than standard 300tdi postion....
However this does cause a few problems...
Oil cooler pipes, intercooler pipework and coolant pipe work will all need extending by 2", the fan cowel will not cover the fan if you are running the standard viscous unit, the air filter pipework will be a little bit tight (but still manageable) and the exhaust will need shortening by 2" (or there abouts) - as the engine will now be 2" further away from the radiator.
A local Land Rover specialst AFAIK does his conversions this way...
Regards the loom... a 300Tdi isn't that different from a NA Diesel one.. and can be easily adapted.
However, again it comes down to if you want every thing 'as per factory'...
The only real difference between the looms (apart from having to extend a couple of wires) is that a 300TDi has a glow plug timer... which you don't really need - you just need to hold the key in the glow plug position for 8 seconds like you do now.
Ian