The fork in the little arch needs to fit inside the pi-brackets in the field frame bars. In the case of cheiroballistra the pi-brackets are pretty small, so the dimensions of the should be just right. Making one bend is easy on any anvil, but making the second bend to the exactly correct position can be tricky, especially if the anvil face is wider than the inner width of the fork. One option would be to do the second bend in 90 degree angle to the first one, so that the width of the anvil face does not matter, and then rotate the other end 90 degrees. Another option, which is described here, is to make a simply rectangular forging form, around which the fork is bent. The only problem with the form as described here is that securely attaching it the hardie hole proved to be tough. In retrospect a welded metal form would have been better.
Making the form Edit
First measure the correct width for the fork using a model fork made from thick metal wire:
Once you know the correct width, take a thick, rectangular wooden beam of the correct width and wrap a thin, wide piece of steel plate around it, and then nail the plate to the bottom of the beam:
The purpose of the steel plate is to protect the wood from blows as well as the extreme heat from the steel. The plate is nailed to the bottom so that the top and side surfaces (shown below) are perfectly flat:
The next, tricky part, is how to keep the form in place when forging. One option which seemed to work well enough was to use metal "straps" squeezed tight against the sides of the anvil using clamps:
The steel rod has been punched through the steel strap and into the wood to prevent the form from moving back and forth.
The form should project outside the anvil face only just enough to allow you to forge the fork.
Here's a fork forged around this particular template, just before it was flattened and welded to the central part of the little arch: