The intake manifold between the heads should be wider. Also the lower thermostat bolt should be higher "above the water pump". Do you know what year motor? From here the motor looks like a pretty stock 351 boat anchor. With stock heads on it it wont make much more power than a 302. But it will have a little more torque. Unless the car is in better condition than what you have i would just stick with what you have. Build your own 351 on a stand and drop it in.