Librands advertise exhaust headers that go straight out of each side, rather than crossing over underneath the sump like they used to - see
http://www.librands.co.uk/products-category-26.html.Another possible source is RPI Engineering -
http://www.ebay.co.uk/itm/Morgan-plus-8-...item2c7463cfee.Not cheap though.
This side of the pond they are called exhaust
manifolds - if you Google "exhaust manifold 4.6 Range Rover" you will find a selection of cheaper alternatives.
Hope this helps.