YES 5.9 Magnum manifolds work in early A bodies. Here is exactly how!

Thanks man that is awesome that gives me all kinds of ideas and options!
You're welcome. Although I figured out a way to make the downpipe on the bench, the easiest way to do it is to install the manifold in your car and piece it together under the car so that it clears everything and fits well. You can tack weld the pieces in place and when you have it exactly in the right place (orientation) you can remove it and weld it up 100 percent. This way it fits your set up perfectly.