Yea man, that's a hot topic around here. Unless you want to spend some major change on some tti's just keep those pretty manifolds you have in the pics.
original headers are bad choice to me. They have small inner diameter.. bad format.
They also have two major problem on driver side. too short space between then and steering box and Z bar.
Concludng, I think original headers do not have a good performance.
From headers to the end of exhaust, I will use stainlles steel tubes with 2 1/4 inner diameter with H between them. Perhapes I will use a cherry bom like muffler. All exahust system will ends just before rear axle
may be a crazy configuration, but I think wiill work nice.. with a really nice sound wich can be comfortable to long travels