my tuned 1242 cinq just went through an MOT with a chip on there. 0.0% CO at fast idle, with 13PPM HC (fail is 0.30% and 200PPM). 0.12% CO at idle (fail limit 0.50% i think). No problems with the chip and MOT. I think Michael has added that about having the old chip for the MOT because last year i had problems with emissions at MOT. Turned out to be an ECU fault, combined with a dying engine - NOT the chip.
Also, the chip leans out the mixture through most the rev range.
Swapping in an ECU from another car, you're going to need the ECU, the codebox, the keys and the lockset.
Not sure if the chip has been tested on the 899 or not. It should work, but might overfuel cos of the smaller engine. also it might be possible to do a custom chip that just has the imobiliser taken out - i dunno though, ask him!