I concur with Paul...
I replaced my ignition box with a stock replacement MSD unit and The change was AMAZING!
It was like it was a new car...
It still popped after a rev but that was from poorly tuned SUs. At idle it ran perfectly smooth all the way up around 7k.
Mind you that is on a L26, roundtop SUs, 11.5 Lb flywheel, MSD5900 unit, L24 flat-top pistons, mystery header-2.5" exhaust, and the stock E88 head with the "C" cam...
Before replacing the ignition unit it stuttered at idle. When I stepped on the throttle at lower RPMs in 2nd or 3rd it would pop and lose power for a second or so when the engine was cold.
Another thing to check is under the dist. cap and see if any of the electrodes or rotor cap are really dirty. That can cause problems too.
All is better with the new ignition..