The problem with Mallory Distributors, at least the YL units, is that the drive gear 1/8" roll-pin can shear. I queried Mallory about it and was told the failure is normally associated with using a high volume
oil pump.
What I did to resolve the problem was to re-drill the roll-pin hole through the drive gear and dist shaft with a #22 drill bit. I then pressed in a 5/32 roll-pin (the split kind, not the rolled up kind) with the split up (down also works) and then nested a 3/32" roll-pin inside the larger one, but with the split 180 Deg apart.
Despite the fact that a loose drive gear to shaft fit is also a problem with the Mallory (you get more bending of the pin), the mod has not failed me since, at least 4000 miles ago.