Something I learned several years ago is that the MSD boxes are sensitive to degradation of oil-filled coils, especially if the coil is horizontally mounted.
Pretty much a lottery as far as time, as those coils aren't completely full of oil.
An epoxy-filled coil avoids that, but doesn't look stock.
On several cars since, I've used a re-curved MP electronic dist, MSD6 box, and F150 epoxy coil, when stock-appearing wasn't necessary.
On every one, the cars will light off almost immediately, run crisply, and run without failure.

It's one of the areas where restoration/originality and higher performance diverge, like headers.