[AshE84]

Hi all, before I start getting all the "just buy the car with the engine in already" comments I'd like to make it clear that in the UK it doesn't exist the biggest we can get here in RHD is the 2.0l N20B20A.
I have a 2013 E84 Sdrive20i with the 6 speed manual gearbox. I recently developed a misfire on cylinder 4 of my engine which after some diagnostics i believe to be the cylinder rings failing. due to this I find myself in the position of either stripping and rebuilding the N20 with up rated parts (because I wanna run about 350hp) which will cost a few grand and may not be the most reliable once done, or what I'm hoping to do, is swapping the engine for the 3.0l N55. From what I can tell it should be doable. I believe the the gearbox fits but I'm not sure what clutch and flywheel I'd need. I know the engine itself will fit as the US and Germany have models with the engine fitted from stock so things like engine mounts/ Rad lines, and Ect can be found rather then need to be custom made.
The main thing I'm unsure about is, would I just need to swap ECU's or would I need to change other computers to get the engine to run and for the Idrive and OBD to work along side as if it came from factory fitted. My idea was to buy a donor car and swap the parts I needed but if all i'd need is the engine and ecu then i may find them cheaper than an entire donor car.
Any advice would be appreciated TIA.