I did headers on my 360 (bought them used) and used 2.5 pipe into a 3" single exhaust on mine. I used the Flowmaster Y pipe for a smooth transition. 3" SINGLE EXHAUST INTO A 3" IN/OUT dynomax super turbo and a late model F150 3" mandrel bent tailpipe out of the scrap pile at work.
The rest was a used performer intake with a quickfuel 650 mechanical secondary.
One of the first things I did was buy a used takeout limited slip unit and 3.90 gears off of Ebay. Should have gone 3.55 but it was a bear off the light with 3.90 gears.