I converted my Cuda to EFI many years ago by adapting the 5.0 Mustang's fuel injection system from Ford. I originally installed this set up on a mild 360 that originally came in my Cuda. I was tired of the Demon carburetor I was using. I was always making adjustments on it and I wanted the precision of EFI. If your car is not going to be used on a regular basis, you might consider staying with the carburetor until you get the rest of the vehicle way you want it to be. Switching to EFI isn't cheap and our older cars could use upgrades everywhere (suspension, steering, bodywork, electrical work, interior work, etc.) I didn't see a massive difference in fuel economy. Putting a transmission in your vehicle with overdrive will have more of a positive effect on fuel economy than switching from a carb to EFI.
Through the years, I've made many changes to my engine. It is now a Vortech supercharged 408. The precision that EFI offers over a carburetor with my current setup is unbelievable. I'm running between 9 and 15 pounds of boost on a 408 that has incredible drivability, reliability and road manners. I couldn't run my current setup with a carburetor. I would highly recommend EFI if you are considering any type of force induction. Even though I'm running 3.23 rear gears and I'm using and A518 automatic transmission, fuel economy isn't great. I get about 17 – 18 mpg on the highway. Again, an overdrive transmission made a more noticeable impact on fuel economy than switching to EFI.
When I converted my Cuda to EFI years ago, there wasn't many aftermarket options. Today however, you have many options to choose from when considering which EFI setup is best for you and what you intend to do with your vehicle.