Joe, do you just want the cat-back for the car or the full system?Cat-back is about £400. See link belowhttp://www.awesome-gti.co.uk/vw%20golfmk5/exhausts.html
Joe,i can't see why not, on my Mk4, that is exactly what i did.The Cat back came with a stepped convertor, fitted great too, for all of 2 weeks, until I got the offer of a Milltek cat and downpipe.