Solid LT1

Rotor should not contact any part of the distributor cap except the carbon center button from coil terminal. If your hitting a contact on outer edge of cap, you will crack the cap.

One thing to note, when your rebuilding distributor, take a careful look at wire on underside of points mounting plate and make sure it is in good condition, this wire grounds the plate through the vacuum advance mounting screw and if that wire fails, your Pertronix unit might get flaky. I use a braided copper product called "solder wick" that is sold in electronics stores to replace that wire. Delco actually used braided copper grounding conductors in older distributors and I have never seen the breakage in those that I see in the later ones with the insulated points grounding plate wiring.