im pretty sure but not 100% but with the emissions side of things im pretty certain its a case of what car its going into and not what engine your using.

for i.e lets just say a 1.8 mk6 escort gti registered in 1998 so it has a cat, then you fit a 1.6cvh turbo lump in the car come. mot time the car will still need to pass the emissions set for the 1.8 which are much lower than the car the cvh turbo came from and you may have difficulties passing.