If you need to use a spacer, go and see your friendly neigborhood Ford dealer (yup Ford) and ask him to order you a Motorcraft part number YS-30 (provided that it hasn't been obsoleted).
It's an aluminum spacer that's used on Motorcraft alternators from the 60's up into the mid-80's. It's easily cut with a hacksaw, and looks far more "pro" than a stack of flat-washers.
I suppose that these are also a "dime a dozen" at almost any auto wrecker as well.
I also found a site that has an excellent selection of bracketry via e-bay...
And hey! Just looking at your picture ... doesn't the bolt usually thread in from the front instead of from the rear?