I work for Autolusso in the used parts dept, and also deal with the Wizard exhaust enquiries/sales, Ned is the owner and you will mostly find him running the workshop.
We modify the original cats on the Mito 155TB to make them flow better, and as well as that we can supply a complete new exhaust from the cat all the way back to the tailpipes in a much larger diameter, to freely flow upto 250bhp. The Mito QV 170bhp is similar, but I've not seen the cat for this engine in the Giulietta yet, so it could be different. Next time we have one in I will have to take a look at the original exhaust system and see how it can be improved. I'd love to see what we could get out of a 1750, I reckon with a bigger turbo, intercooler and better exhaust, 300bhp should be easy.