From what I remember the 350-2 came with single exhaust and the 350-4 could be had either way with the appropriate check box on the form. Don't tell anyone, but the GS California came from the factory with single exhaust! Imagine that 280HP 350 trying to huff through a little 2" single pipe!
separate pipes, one from each exhaust manifold, exiting on each side under the rear bumper with a nice turn down and angle cut tip.