All of these systems are going to have limitations for varying reasons.
The aftermarket EFI systems are using existing sensor components already in use from other vehicles.
One advantage is easy walk in parts availability and also cost. Using production GM parts is a great advantage.
The MAP sensor used in any of the systems is going to be key for the ECU in determining the "load" on the engine. That is used in combination to the engine rpm and the oxygen sensor.
With a camshaft timing of over 250° @ .050" lift, the MAP may not have the ability to sense the engine load correctly and add too much fuel to the injectors at only a partial load? That is probably the biggest factor in causing "fouling" of the plugs BUT that may not be a 100% accurate assesment?
You may need to run a one step hotter spark plug and you may need to alter the advance curve of the distributor?
A big port iron 4v head Cleveland is going to be the toughest to get the fuel curve right on with. I wouldn't go assuming though that you can re-write the curve in the computer. You likely will make it worse.
The cam you are using is a bit over the limit for a primarily street driven car. The cam that I am using is at 244° and I am thinking of dialing that down one step already. That is more of a "track day cam" for a car driven to and from the high speed track event.
It sounds really cool but is more of a "boy racer" thing and I'm getting way to old for such an adolescence based showboating?
I think that most likely dialing down the cam timing on a flat tappet lifter cam to the perverbial 237° @.050, or going to a roller lifter like the Ford Racing 304X cam will coexist better with any of the EFI systems?
You are asking for information that only custom tuners have experience on and have arrived at on other vehicles and likely unique to those vehicles as well.
When I ran Holleys on my 351c's, there was always this issue of getting the a/f ratio just right. It was never really a battle with the carb jetting, it was more an issue of matching the ignition power, advance timing, fuel quality variations and plug heat range to get the plug color just right at dark rust brown v. black and sooty.
One custom tuner thought that it was just an issue of the ignition spark not being strong enough. i.e., a "weak spark".
All I can say with that, is good luck because I don't think a perfect tune exists. For one thing, it will literally change with the weather. You may be a better man then I though, so go for it.