5th Avenues never came with dual exhaust but a lot of people like the way it looks or like adding it to cars to get more power. This information is from Hutch who originally posted it in Farley's forum.
Headers are Summit # SUM-G9040 for F-Body $99.95. They look like Hedman design, and they fit great. Tubes don't hit or rub anything. Installation requires the usual: Right side - Remove the oil filter adapter Left side - Get beer. Remove steering drag link, starter, trans shift and kickdown linkage; loosen left motor mount bolt and jack up engine 3 inches. Exhaust system is Jegs # 555-30500 2 1/2 inch for A-Body $219.99 including turbo mufflers. This kit runs out the back so gas tank relocation is required. The kit fits with no mods and can be clamped or welded. The pipes run straight out, but I cut them off short and added 2 1/2 turn downs - $4 ea Advance Auto.
Standard 3 tubes under the steering linkage.
The turbos are pretty quiet at cruise and sound good with the go pedal on the mat.
Tank moved. Filler tube has to be lengthened too.