Electronic Injection
The only complete off-the-shelf EFI setups for the Holden six that's suitable for competition use that I'm aware of is the one made by Sonic Injection (see links section). For accurate metering over a wide range of speeds and conditions, a well tuned EFI system will be unbeatable - but note the use of the words "well-tuned". A poorly tuned EFI will be just as bad as any poorly tuned system.
Because the injectors regulate the amount of fuel injected by varying the amount of time they are open (rather than by varying supply pressure) it's possible to get a good spray pattern and mixture quality even at very low speeds and at idle. Injector pulse width is determined by the ECU, which calculates the value using inputs that may include mass air flow, manifold pressure, throttle position, crankshaft speed, coolant temperature etc. Systems for competition use are often simplified to use only crank speed, throttle position and/or manifold pressure.
Building and tuning a good EFI system will cost a bit more than say triple Webers and it does add some complexity, but because EFI is so ubiquitous on modern cars EFI expertise is probably now more widespread than that for carbs. Interestingly a carburettor will often show as much power on a dyno as injection, but on the strip a properly tuned EFI will be markedly quicker. In summary, a well done EFI system will provide the best performance in nearly any application.