Fast ratio boxes refers to manual steering, unless it's the new Delphi based unit for amazing money. There is an old thread in the handling forum on them. I'm not seeing a box for a 70 Cuda on their site so I dunno.

The arms are cheaper but they can hit headers not designed for the added length of the arms.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.