Last year I had a mechanical restoration professionally done on my '67 300, to include rebuilding the 440 and 727. Everything was original. In lieu of the carburetor and distributor, I went with the Holley Sniper EFI (the first version - Sniper II was not out yet) and their Hyperspark distributor, an Edelbrock Performer intake, and TTI headers and their full exhaust. The forged crank, rods, and 516 heads were reused/rebuilt, pistons are aluminum flat-tops, and the cam is mild. Overall the build is on the milder/streetable side, since my ragtop is for cruising not racing.
So glad I went with the Holley upgrades. Starting is reliable, whether the motor is hot or cold. Drivability and power are great. The computer will "learn" - but only so much.
@Knebel is right: get the Hyperspark distributor, and you will need to download the free Sniper software and tune it yourself on a computer to get the most of out of it. You'll be glad you did. It only runs on Windows, so if you're an Apple guy like I am, you'll need to buy a Windows computer.
Just as a quick example of why you need to tune on a PC: you can set the cruise timing on the Sniper handheld that comes with the unit, but the cruise timing for me would only start to kick in around 2500 rpm. With my axle ratio (3.23) and rear tire size (255/70R15) I do a lot of cruising around town at around 2000 rpm (~45 mph). So my cruise timing never kicked in and fuel economy suffered. Now that's not the case, since I am tuning on the Windows laptop; I have lots of advance in the motor at 2000 rpm and it runs great.
I am still on this learning curve myself, but having started tuning the A/F ratio and the timing a few months ago, I can already tell it's better. The motor just wants to keep pulling, and the fuel economy is better (14 mpg vs 10 mpg with the learned computer "tune"). I have about 42 degrees of advance at cruise, 35 degrees at WOT, and if it pings I can reduce it easily. I have the A/F ratio at about 14.7:1 at cruise, and I am slowly experimenting with leaning it out to improve fuel economy.
I am making small adjustments now each time I tune it. If you keep a known good tune that you never delete, you can always go back to that file if you screw up (which you inevitably will). You can keep multiple tune files on your SD card, so if you don't like the new tune you can easily change it back to the old one right from the driver's seat in a matter of seconds. It's easy.
You can also data log: record files of what the motor is doing (rpm, timing, A/F ratio actual and target, coolant temp, and on and on) at cold idle, hot idle, cruise, WOT, etc., so you can study it later from the comfort of your living room and figure out what is working well (or not) and adjust accordingly. It's easy (did I repeat myself?).
Just make small changes and go easy on the motor so you don't blow it up. There are lots of YouTube videos that will guide you. I found Joe Simpson's videos very helpful.
A final thought: my son will inherit this car one day. He loves it but is not a mechanic and will have no interest in tuning a carb or setting timing. With the Sniper, all he will have to do is turn the key and drive it.
Hope this helps.
