My choice is to weld hooks onto a flat plate, maybe 4" x 3" and then weld the plate to the bucket. Special hooks are made just for the purpose. Google "weld on grab hook". There are straight ones and ones set at an angle.
Weld them between the arms of the FEL or directly in line with them. Hooks outside have a tendency to skew the arms if heavily loaded. Plus, lifting from there makes the tractor tippy.
Look at where the chain will go over the top edge of the bucket. If it is a standard bucket with a bend over the top, rather that a heavy tube, see if you can find a piece of pipe to weld into the fold so when the chain is loaded it won't crush the bucket's edge.
Use whatever support and braces that are already on the bucket to choose the hook's location. They will supply more strength.
Consider a hook on the back of the bucket closer to the front of the tractor. You will get more lifting leverage there but there is an additional danger of something swinging into the tractor. Hopefully you have or are considering a radiator guard.
A hook on the backhoe bucket is no problem. Use 3/8" hooks at a minimum. A backhoe can yank quite hard. Obviously, attach it to the back of the bucket to keep it out of the dirt. There is no reasonable way to bolt one on to a backhoe bucket so be prepared for some welding.