Hi dan,
I have this conversion underway At the moment in my garage for a friend.
The 110 is 12v, like said before, just check the bulbs, if there is no obvious second battery, or even the "this vehicle is 12/24v" decal on the rear crossmember.
As said previously, If you have a 200 tdi then its easy, dont use the auto box, unless you really hanker after an auto.
Use the original g.box, assuming its a 200 tdi, take off the flexplate, ( where the flywheel should be, as its an auto) take off the flywheel casing, at rear of engine.
Use the casing and flywheel from the defender engine, makes life so easy,
Hopefully you kept ancilleries from the tdi donor. Fuel connection (banjo) on pump is different.
Change the engine loom from the defender to the tdi
Then dont forget you will need to change the radiator, for a tdi rad and intercooler, unless you go non turbo with the tdi, but this, although reliable, is then not that much more power over the 2.5 t.diesel.
Use the engine mounts from the original engine onto the tdi
You should do a build up thread and post some pictures, i didnt think about it until i was part way through the conversion.
Hope this helps
Cheers
Shaun