Distributor rotor button freeplay?

Take a look at the burn pattern where the spark jumps from the rotor tip to the cap terminals..Are they centered, or way of to one edge? I found a brand new (part of a dyno'd Indy crate motor) that the cap or rotor was not indexed properly. I modified the cap to get the burn centered in the terminals. It helped a poor idle condition. You may want to verify the advance limiting bushing is still in place, also look at the bushing and oil pump drive in the block. I pull the drive out, and if there is any wear/taper/scratches, replace it and the bushing. It can be a little tricky with the engine together in a car, but you need to make sure not to drop any oilight bushing bits into the oiling system, and that the new bushing isnt too tight on the drive after installing.