Reprinted with gracious permission from original submitter, bikebuilder, from this thread . many thanks to bikebuilder!
Someone asked me to explain how to do this. This particular brake setup is the easiest to modify. The one on my bike was more difficult. The center mass or the "ball" on this one is in two peices. All you have to do is weld the two peices together so that it cannot reset it's self while riding. Reassemle the hub and weld a lever on to where the gear used to be with holes front and back. front for the hand lever and the back for a spring. Make sure that the lever you weld on is in the best position possible to work with the hand lever.
The one on my bike had the ball in one peice already but did not have that little peice sticking out between the pads to hold it in place. This would allow it to reset. So I had to weld a little nub on the ball.
This conversion works pretty good. I can leave black marks with the one on my bike. The one I put together for "little brother" 195lbs would lift the back tire off the ground.
You can see it in use a little watch the video linked in the rat-rod swingbikes post
ratrodbikes.com • View topic - Rat-Rod swingbikes