You could get backbox, centre (deresonated section) and delete the third cat with NO Mot/ emissions problems.
Personally I'd recommend (I would[]) a group N back box 4" rolled tail, to go with centre section and de-cat pipe. Releases the burble nicely without the blue lights following ie decent sound doesnt wake the street.
My mate Paul makes all of these and I can get them @ great prices for Scottish Scoobies members.
Gus