Rally-pac's were standalone factory or dealer options and not grouped with any other option.
The behind-the-dash harness for a rally-pac is just an auxiliary harness that plugs into the main harness. So, even the presence wouldn't necessarily confirm your car had a rally-pac when new. Although, if the wiring was original FoMoCo and appeared to be un-tampered, the probability would be higher.
Since these were commonly dealer-installed, we see variants in the types of interiors. Generally, the high-profile style rally-pac was used with the falcon-style instrument cluster and was always (supposed to be) black crinkle finish. The low-profile was most typically used with the 5 dial instrument cluster, found on GT standard interior or deluxe interior cars (that were GT's too.) The low-profile could be color-coordinated to the steering column color or simply black.