Hears what I did to my 73, I put a 514 inch 530 torque engine, Aluminum Heads very important to lighten the car, C6 transmission 11inch converter and shift kit, 3.50:1 posi traction, 10 inch wide tires, put the car on a diet got it down to 3100 pounds. ran easy upper 12s.
73 mustang are easy...