putting a cat on a 71 would be a waste of time and money , plus there is no roon for it , later pintos had the floor notched out to make room , only a few inchs , a after market cats are a tad larger than the stock cats for a pinto , you have a muffler problem , a cat on your car may cause problems , the carb for the 2.0 runs richer and may clog the cat over time , you may have a cheep stock looking muffler , not the best , I know that the fatory muffler on all the pintos I had over the years were very quiet , the 2.0 should be easy to find a good muffler for , your best bet is to find a old muffler shop that still run by the owner that knows muffers , you can,t beat experience . good luck