There were actually Formal Roof and Fastback Roofline Sport models built. I have been able to find out through research that about 51,000 Fastback Sports and 17,000 Formal Roof Sports were built in 1973. I would like to find out the option/production breakdown though. I did see a fastback on ebay for sale one time that was a 4spd and the seller stated a production of 1700 but I'm not sure what his source was. I am just assuming that going by his numbers and the production difference between formal roof and fastback models the 4spd formal roof models would be much rarer.