I suggest calling Stan at Ford Powertrain Applications out west in Washington. He does custom headers for Ford powered vehicles. His main market is the restomod crowd that sticks a rack and pinion steering sytem under a classic Mustang, Cougar or something similar.
If you can get someone who has a car with the headers you want to take a few pictures with a tape measure from various angles, they MIGHT be willing to do something.
I have two sets: Ford FE in a 1970 Mustang with a Randall's Rack, and his headers for a '56 T-Bird with a 312. They're pricey, but well worth it from a materials and craftsmanship perspective.
http://www.fordpowertrain.com/FPAindex/FPA%20index1.htm