Exhaust can be another tricky part of your LS Swap. Depending on your frame, suspension, and other factors, you may be able to run stock manifolds, or you may need to order a custom set of headers. Either way, there are lots of options.
If you want to try stock parts, you can always start by trying the stock manifolds. Trailblazer SS manifolds are often used due to their compact, yet performance minded design. Others utilize F-body manifolds.
If you want to go with a set of headers, the possibilities are nearly endless. There are a number of companies who make long, short and mid length headers for GM trucks and cars that may work for your application.
Once you get past the headers, you’ll more than likely need to have a custom exhaust system built. If you have the skills, by all means break out your welder and get to work. If not, your local exhaust shop should be able to build you a system to meet your needs.
Whichever route you go, be sure to weld in bungs for the front O2 sensors.