Radios were not standard on any '71-3 Mustang. If the dealer or customer ordered no radio, they came with a radio cover plate in the radio location and no hole in the fender. The cars went through a "PDI" process (Pre Delivery Inspection) where the tech checked the car for options and standard equipment being correct, fluid levels, and loose or missing nuts, bolts, or hardware. The trunk would contain wheel covers, floor mats, and the radio installation kit (if ordered with any radio option). The installation kit would have the radio, antenna with the fender drill template, and all the hardware needed. Only the higher-end cars, such as T-Birds and Lincoln, came with standard radios and factory-installed antennas. This continued through the late '70s. As each model line was redesigned, such as the new '79 LTD and Mustang, they had antenna hole cover plates on the fender if not ordered with a radio. This was seen most often in fleet, police, and taxi vehicles. A lot of people would not order a factory radio so they could have a custom system installed. Accessory sales were a cash cow for dealers. Many dealers utilized companies that specialized in installing audio systems and other accessories and would come to the dealership to install them. Many radio opening cover plates were tossed after a radio install and now command insane prices.
The power antenna was a dealer-installed over-the-counter part and was not production installed on the Mustang.