But the bottom line is, a 273 that runs 12s in a 3200lb street car is going to be a tough build. More expensive than a 318-340-360, and less torque than any of them. It will basically be a temperamental race engine that you try to make street friendly, and will likely be a exercise in dissatisfaction. Put a 4" crank in your current 340, refresh the engine as needed, and be miles ahead and have money left in your pocket when your done.