Carbs are great...BUT:
where EFI really shines is tuneability and driveability. You can get the same maybe better fuel mileage with a carb, but with EFI you can run it leaner (cleaner) and still maintain excellent manners. With a carb, once you get to around 15:1 A/F at cruise speeds, sometimes you will run into a slight surge. Because EFI controllers (the ECU, computer, whatever you call it) operates at such a high speed compared to a regular carb'd motor's ignition system, it is capable of monitoring ignition misses, changes in A/F according to the O2 sensor(s), and adjust fuel injector pulse width....many hundreds of times per second, which usually makes for great street manners (again, compared to a properly tuned carb). Then, if you need to change the fuel or ignition map, you don't even have to get your hands dirty. Just a few pecks on a keyboard of a laptop and you've changed the engine's whole attitude.
I did a Megasquirt on a 2.3 Turbo in an SVO a while back. MS has advantages, and most importantly for me was price.....and it's tuneability, but I sold the car before I ever got it fully tuned. I never got the cold start enrichment set up to where it was as smooth as the factory EEC was, and from what I've read, it's tough to duplicate the Ford's cold start system. I sold it with the factory EEC and VAM system installed...worked fine, but had it's limitations. About 300 HP is the limit for a stock 2.3 with 35 lb injectors and around 20 PSI boost. the MS system I had on it had 52 lb injectors and I was playing with around 24 psi. Don't know how much HP, but man it was a ride---for an old pinto motor. Now, I guess you "could" use a 5.0 EEC system and use an old EFI 7.5 distributor...but you still have to get a intake manifold modified to accept rails & injectors. If it were me, I'd make my own manifold....2 separate throttle bodies on 2 separate manifolds, one for each bank. Then use the Ford EEC-IV 5.0 factory MAF system. Should be fairly easy since the cleveland uses a dry manifold (no water passages).
That said, if you're considering EFI, be sure to consider the costs and downtime. Costs can get pretty high depending on what system you use. I had about $550 in my Megasquirt and I bought the controller pre-assembled. You can get them unassembled and set it up how you like for a little less money. The carb is the simple, safe, and tried-and-true way out, but it a little less sophisticated...but also has it's disadvantages. For mileage concerns, a carb and ignition system can be tuned to get great mileage....and so can EFI systems, but I'm still pretty green with EFI to be able to match the kind of gains I saw with an old Edelbrock 1405 on my old '84 Mustang GT. With a mild built 302, at one time it was getting over 35 mpg---fill the tank with 10 gallons and drive 350 miles, fill with another 10 gallons. I never got better than 28 out of the SVO, but then again...I never kept the boost gauge on the vacuum side of zero either.
So, in a nutshell....pick your poison. both have their advantages & disadvantages.
