Despite a US-spec Pininfarina Spider being fitted from new with a cat, this won't be required in the UK. No 1985 car will fail an MoT for not having a cat in place. Unless you're fastidious about originality, we'd be tempted not to reinstate the cat, as the car is likely to run better and be marginally better-performing without one. Our temptation would be to focus on a cat-free exhaust system, either adapting the one you have (maybe fitting a new rear section to prevent it fouling on the suspension) or investing in an all-new system. Talk to Middle Barton Garage (www.middlebartongarage.com) and DTR European Sports Cars (www.dtrsports.com) regarding new exhausts.