Gauges means it has the tachometer and the oil pressure and water temp gauges versus just the empty round idiot light bezel that was the same size as the speedometer. In 1972 the 455HO Formula came with the unitized distributor as a mandatory option but the T/A came with the points distributor standard, with the unitized distributor as an extra cost option. I dont know about the 400 engine, though, on the Formulas.
Do you have the PHS invoice sheet on your car? It would show the unitized option on it.
For harnesses check out these guys:
http://www.lectriclimited.com/mainpage.htm