Catalitic converter

does anyone know why my 92 Ranger has two catalytic converters, one behind the other. I'm in the process of buying a whole new exhaust system and would like to know if replacing my current setup with a single cat converter would screw up my emissions. Also what kind of converter can I replace it with and how would it clamp/bolt on? I've been quoted at having to pay damn near 200.00 for just a converter where in J.C. Whitney they have converters starting at 70.00
Thanks to all in advance