Getting attention but no miles...still, it's being kept dry(ish) so shouldn't deteriorate too much.
Engine swap is fairly simple, but you need some way to drive the BX hydraulic pump unless you switch to the Xantia FDV-less setup (or have an early donor engine). I used an N/A cam kindly donated by Talbot, must be around 10 years ago now. If the donor engine had a vacuum pump (ZX/405), you need to blank off the oil feed to that otherwise it will get very messy!
Clutch and flywheel need swapping from the BX unless you want to keep the Xantia pull-type clutch for some reason. The puzzle I found when I first got it running is that to run smoothly the Xantia engine needed the glowplugs kept on after starting, so powering the glowplugs with the BX relay give a rough and smoky idle for the first 30 seconds or so. Swapped to the Xantia relay and all was fine.
If you look closely, you can see a certain blue Discovery in the background, before the rollover!