The best way to use oem mag manifolds is to find a drivers rear exit and a pass. front exit, passing the cross pipe aft instead of forward. This way you can retain power steering box and column, easily.
Its been a long time since i looked at it, but im 99% sure the magnum manifold even in the correct intended mounting location does not clear the factory a body power steering box.
Also there is very little room for the down pipe, and the cross over on the pass side if you do it this way.