Ok. So im looking at exhaust for my:
1993 GMC Sierra, 5.0L v8, regular cab long bed.

I am looking at a 3 inch cat back kit. And it says it is 3 inch. (NICE!). It includes muffler and dual pipes. But im wondering if i have to modify anything or if the 3 inch kit should just fit on the stock system.

Answers please?

 

Slam dunk! If you go with a reputable kit (flowmaster, magnaflow,etc) they do come complete! Get your rig up off the ground to give you more room to work, and go to town. If you can't weld, clamp it all together and shoot down a local muffler shop and have them tack all your seams.