mtx could be done for far less.
mtx box £100
strip and rebuild £300
atb diff £600
so for a grand you've got a good box.

selector setup £50
hydraulic clutch setup £100
new bigger clutch £400 or less depending on make etc.

custom drive shafts circa £200-300
so around £2k if i do the maths with someone fitting it i reckon, not a lot of work involved really and the same route my xr2 zvh turbo will be going after the wedding.
Although i'm just going to fit a non atb box in first just to get all the parts sorted, so around £1k then spend on an atb diff later and rebuilt box.