Bilstein Shocks
If you clean out the grease and crud from the torsion bar mounts from the back, you should be able to read the last three numbers and get the size. Formula S Barracudas and 340 cars came with the .88 diameter bars. There are guys that sell those cheap here. The .88 torsion bars, good shocks, good rear springs, sticky tires, and a front sway bar should put a big smile on your face. 64 "A" bodies are pretty light, I had a 64 Barracuda that I did everything to.