Just weld on a 4 bolt flange and add what ever length you need to it. That way you have a NEW one that has not had ANY leaded race fuel run through it. The factory cats are real good at Emission testing, but if they have had even on gallon of leaded fuel run through them at any point, their effect is severly deteriorated. The flanges are available from RJC. Any local weld shop can also handle the welding for you. Great little converter I linked, and at $50 you can't go wrong. Add a flange from RJC. #RJC-CATF-S for $29 add $25 for welding and you have a new converter for a little over $100. The high flow version is $138. But, if you only need it for an emissions test, buy the cheaper one,