What would be the load per sling, sling size and shackle size for A, B and C?

Creating a sling can be complicated especially if you do not know what your main goal is going to be. The correct sling can be made with the proper angle depending on what you want to achieve. The number of legs that can lift up the sling will also be a factor in how effective and strong the sling is going to be.

When the right computations for the sling will be created, it will be easier to utilize the sling material that will be used. There are different sling materials that are available. It would be up to you to pick the one that will work best for the needs of the sling and the items that will be carried by it.