JaNeily, I've seen them and have them done 2 different ways. The old method and in my opinion the best, was actually cutting the manifold in half. Welding the ends closed, and putting an additional outlet on the half that didn't have one before. This method is similar to making a set of headers out of the stock manifold.
The second method is to put an outlet on the opposite side of the original outlet (towards the firewall) and weld a plate inside of the middle of the exhaust manifold. (My 46 has this type.) There is a small diameter hole in the plate (inside of the exhaust manifold) to equalize the pressure, between the two separate (but still together) halves.
Hope that helps answer at least part of your question.
I have one like I described in the second version that I can take pictures and send to you if you would like.
As for the other, I'm sure if you look hard enough, you can probably find a picture of the actual split manifold. If not, I know there are pictures of fentons (headers) around the site, and they would be close to how this type of split looks.
