When it comes to being "fast"...define what you mean by that-is it a dog? Does it not run as fast as you want? How fast is fast to you? 11's? 10's? If you have a well tuned 331 with Edelbrock heads and a high rise dual plane intake (Edelbrock RPM), then your problem is probably because the carb is too small or jetted wrong...you might have other tuning issues, you said nothing about what kind of transmission your running, or what rear end ratio, what size tires, exhaust, ignition timing...
Basically your information is very vague...you need to define expectations and a goal. I've seen and ridden in stroker powered cars with similar builds that were absolute turds until properly tuned-this applies to carbed vehicles too-not just EFI fed versions. But, a good running 331 in a little '66 ought to move down the road rather smartly if the car is configured correctly. The cam, by many standards, is pretty old tech and probably isn't the greatest grind for a stroked 302, but nonetheless it should make decent power up to about 5500 or so...
Can you reply with a better idea of what all you're working with? And please disregard the whole '86 thing...your combo is already built and its a moot point that doesn't affect you. 331 means that you have aftermarket pistons that will already have a proper amount of valve relief for pretty much whatever you wanna run. I can't think of a set of 331 slugs that don't have enough relief for at least a .600" lift cam.