grand marquis catalytic question??

i have a 92 marquis and it has the cat system that utilizes 4 cat converters,two together right on both sides before y- pipe,the new systems have done away with this now and only use one before y-pipe,question is the garages want at least $300 per side to install,but quite a few parts dealers including napa,pep boys and such are in the $150 to $200 range for direct bolt on fit,at over $200 savings on the parts end of doing it myself,does anyone know what would be involved or snags i would encounter? any advice on getting the flange bolts loose or knocking them off or special tools or technique needed?? money is tight and i kind of need to tackle this job myself, thanks if anyone can help or offer advice, bob