You are correct on that not being the final exhaust. It's just rigged up move around for right now. He will be running dual stacks up through the bed, so picture it with a stack (same height) by the drivers side as well.
Had a buddy years ago with a square body and a 502 out of a caddy. He back halved the frame, narrowed the axle and ran a dually setup, all inside the bed. Was :bawss: