New VR for Pertronix III?

Here's an update - got the solid state VR in; so far, so good. Went to install the Pertonix this weekend and it didn't fit! Stock cast iron heads too. The OD is bigger than stock and it was contacting the casting ridge on the edge of the head. Had to grind down the ridge a little but now it fits. But by the time I painted the bald spot it was getting late so it hasn't fired up yet. Should be this week sometime.