a Magnaflow 94000 universal series piece, not because I push them but they have an extensive selection to choose from, and they are reasonably priced.
As for *direct fit*...that's a bit of a play on words. the cat still has to be welded into place....
can't recall if the downpipe on the smaller 3.1 is 2" or 2 1/4"
http://europe.magnaflow.com/02catalytic_converters/02product/universal/universalcat.asp?parttype=UNIVERSAL CATALYTIC CONVERTER&partnum=940