Have you replaced the distributor, or the distributor cap? Sometimes the play in the distributor bushings is enough to cause weird miss fire, or the pickup coil is bad. With how random it is, and how it runs fine in between, I bet it is electrical. It sounds like the only thing you haven't replaced is the hall effect sensor. Check out the side to side play on the metal pin wheel, and check the gap clearance between the pin wheel and sensor. If you have no play and the gap is something around .020-.045 you could try replacing the hall effect sensor.

If you think it is carburetor, next time it sputters, try giving it a little shot of ether, or pulling the vacuum line to the brake booster. if either of those work it could be carburetor.