Surely if you found a 17mm nut as per original, unscrewed the bolt, screwed the nut(locknut) onto the bolt then screwed the bolt back in that would suffice. I think you may find the rear Alfetta calipers use the same allen headed bolt as the rear Alfetta calipers are essentially similar to the Alfasud fronts and manufactured by the same company ATE and are more readily available than Sud parts.
Richard J
`65 Giulia Ti, `69 GT Junior, `74 GTV 2000, `76 Alfetta GTV, `77 Alfetta GTV, `81 Alfasud Ti, `84 GTV6, `90 164
Richard J
`65 Giulia Ti, `69 GT Junior, `74 GTV 2000, `76 Alfetta GTV, `77 Alfetta GTV, `81 Alfasud Ti, `84 GTV6, `90 164