I am surprised you have not got several replies. I have purchase a couple covers for Mach 1 from this company and one for 1950 Ford. They fit like a glove and no complaints, even have pockets for mirrors. You need to pick the one for your needs. If only inside you don't need waterproof. The prices vary so pick what you need. I don't think they come with hole for antenna but have a reinforcement in that area to allow cutting. I did not read the latest ad might be there. About once a year I would take mine to laundry mat and use a big dryer to tumble it to get the dust out. I think mine came with dusting mop for using at shows to dust the car.
http://www.beverlyhillsautocovers.com/car-covers.html?find=1973-ford-mustang-mach-i-2822929
David
After sending info about the covers I went back to their site and they have great sale and free shipping for just a couple more hours. Mach 1 cover 89.95 for mid price and in the 40.00 for lesser. Convertible same price I actually ordered 4 and it was only $224.85.
The last one of this brand I ordered lasted at least 15 years in a pole barn so pretty tough. Great deal have to act fast.
http://www.beverlyhillsautocovers.com/car-covers.html?find=1973-ford-mustang-mach-i-2822929
David