Mine was fitted by John MacDonald (now Beamish Morgan) and checked before and after on the dyno - but in my case and probably yours no tuning is needed or even possible as the Zetec ECUs appear to be impossible to re-program. The ECU will learn to respond to the greatly reduced back pressure.
I believe Librands have now changed to a 400cpi cat which is less likely to cause MOT problems. Mine is the earlier type which has 200cpi and requires to be run up to high temp to pass the emissions test - but it always does on the 2nd or 3rd pass so no worries.
