Hello fellow Y blockers.

I have a 57 Tbird with a 312 that has developed a misfire at idle when in drive. It does in park as well but it is not as severe. When I pull up to a light the car is idling smoothly and then gradually it will start missing. When I pull away it stutters a bit but once I gather a bit of speed it is fine. No high RPM misfire. My plugs, wires are 1 year old. Distributor cap contacts look good - no pitting etc, rotor looks good. I have the Pertonix ignitor and Flamethrower coil. My plugs are gapped at .046. Any suggestions? On another note does anyone recommend the Autolite Platinum spark plugs If I need to replace them. Any advantages? Thanks