I know its not quite stirling area but I would recommend meercat exhausts in kilbirnie who custom make up the exhausts to suit, I had a 200cell cat fitted by them, its the downpipe and 2nd cat all in 1 section, Havent put it through an mot yet but should be no probs, other than them I have not had any experiance with anyone else sorry, maybe others on here can recommend someone, hope you get it sorted bud.
Stevie