I know that Racer Walsh makes headers for a lot of 4 cylinders including the 2.3 in many different vehicles and configurations. I don't know if the bolt pattern is such that you can flip them like the chevy guys can but I am assuming not. My first first recommendation is to get whichever header Racer Walsh has that you like, use something as a template like clear plastic (mark out wich end is bottom and wich face is the engine side and the other the header side) cut out the header bolt oles, you may want to just mark out the flange face but not cut it out. Take this template and rotate it the way the header is to be flipped and mark out where the new holes should go in the header. double check that the port flow is not restricted by this, I don't know if the exhaust port shape is the same all the way around. If you think there is enough meet to drill new holes and not cause warpage, do so. If not, you may need to make up a special piece that sits behind the header flange so it sandwiches the flange to the block. I have seen some header makers use this to reinfoce the flange.
Another option is to take your header, cut it or have it cut perfectly at square, rotate the flange piece and weld the pipes back together. And there are the do-it-youself kits to. Check with the header companies, Jegs and summit for these kits.
Racer Walsh, Inc. Exhaust
2.3 headers for 1978 Ford 2.3 
