On all the range rover forums there is alot of discussion regarding putting the 6 speed zf box from the 3.6 tdv8 into the td6. But could it be done the other way round, and put an M57 into a 3.6 tdv8.
Told you it was stupid.
Any thoughts?

Anything is possible with enough time/effort/money thrown at it.

However, why would you want to?

The M57 is noisy, underpowered, slow and inefficient when compared to the TDV8 that replaced it.

When the TDV8 came out the L322 moved away from the BMW generation of electronics as well so you'd likely have huge hurdles to overcome. Given how little you can buy a TD6 for these days, you'd likely be as well changing the whole car. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior