I installed some DNA Motoring HDS-GY99 Stainless Steel Exhaust Shorty Headers a while back and got lucky with only 4 broken exhaust manifold bolts. I managed to get most of them out by welding a nut on them wrenching them out, but the rear driver side was too hard to get so I just used the Dorman repair clamp on that one. I also did the WWP Dual Tip Exhaust / Resonator Delete Kit and a Magnaflow 12909 Muffler. The sound everything added is subtle until you get on it...then it's awesome and it definitely added some low end torque.
While I was in there I went ahead and did the ACDelco Iridium Spark Plugs and put the ACDelco 9748RR Wire Set and wrapped them in some titanium spark plug boot protector sleeves.