MSD spark boxes--and their competition--are really-good at covering-up improper carburetion.
In other words, carb runs too lean at idle, leads to lean-misfire. Install MSD, improved spark fires the too-lean mixture, engine runs better. Everyone thinks MSD fixed an ignition problem, when the truth is that it made a carburetion problem "go away".
The better fix is to adjust the carburetion fuel curve so it doesn't misfire.
MSD was NEVER as reliable as they want you to believe; although I think they got worse in recent years as they offshored more to Communist China. Thirty years ago or more, they were selling switch-boxes and coil selectors so racers could install two boxes and two coils, so that when one failed, the driver could flip a switch to activate the other ignition system and hopefully finish the race.
I've had an MSD 5 failure, and an MSD 6T failure. There's a 6AL in my 'Camino; but I dont' think it's got 2000 miles on it in thirty years.