Find out what broke it to start with. I had one do this and broke the new frame right away. Turned out that one of the 2 gears the ride the disk was binding up. As the shaft thought both knotter frames turned this cause the one locking up to rotate up with the shaft breaking the knotter frame.
At that time you could still buy the 2 gears, one for the billhook the other for the twin disk from New Holland for around $35.00 each. The frame was $250.00. This was just under 20 years ago.
Ended up buying a $600.00 complete parts baler to fix the one I had.