Hi, I have a RHD UK 330. It does have 4 cats total and produces 231hp.
The RHD headers are different to the LHD design, I consider them less 'pinched' where the 3 ports join to 1 before they go into the cat. If you look at the LHD headers you will see what I mean. However the RHD headers head upwards and towards the front of the car before doubling back so it's probably even.
Considering your car is LHD you have many aftermarket options available, remember that the RHD headers DO NOT have all the holes drilled for studs in the head. If you look at the flanges in the link you posted you will see there are gaps in the stud pattern. This means you will have to put those studs there (i.e. drill and tap the holes) or use a header that has joined-up flanges.
I'll try to answer more questions later
'04 330Ci Clubsport | Estoril Blue | 6MT | Black Leather/Silver Cube
Turner Motorsport | Ground Control | Stett Performance | Moroso | Powerflex | Meyle HD | Goodridge
Last edited by Dan330Ci~; 10-16-2011 at 01:32 PM.