olblu,
The shackle mount can be repaired by welding and machining a new hole. I am pretty sure the mounts are cast steel; not cast iron. It would be much easier to remove the mount and do the repair; then reinstall it. Depending on your location, you might try finding a good used one. There is a guy on the swap meet board that is parting out a bunch of Chevys and GMCs. I have contacted him about some parts; he would probably have a mount. He is located in Northern California; his name is Jay.
