I think I misread your original question. Do you need a fuse for the component you're installing, or just power off the fuse block?
If you need a fuse, then I change my recommendation to the same as 22GT: use the threaded rod at the back of the ignition switch and use a separate fuse for that component. In-line AGC fuses are easiest to find. That way you're not going to blow some other fuse because you have two components drawing power off a fuse meant for a lighter load.
What, exactly, are you installing?