[Gordonjcp]

> ECUs and dashes on most VAG (VW Audi Group) cars are coded to each other and have been for around two decades if not longer

The mid-90s electronics in my Range Rover will cope with swapping dashboards by programming the mileage to be whichever is highest between the BECM and dash. It'll moan about "ODOMETER FAULT" for a bit but eventually it'll just give up telling you and set them to be the same. While it's possible to reprogram them it's extremely nontrivial, and no commercial units exist that can do it - and the poke-and-hope brigade that offer "mileage correction" will almost certainly leave you with more problems than you started with.

The electronics in them are very similar to late-80s BMW E32 7-series with a bizarre mix of Motorola, NEC and Intel parts.