idle rich, then leans out on highway?

Poor running with excessive gapped plugs is a possible cause of the way the car is runing. Same for the rotor; many of the new aftermarket rotors don't give the right gap to the distributor spark towers, and some will even hit the spark tower contacts. I would steer you to www.slantsix.org and the engine or electrical sections for discussions and best info on spark components for the /6.

Look at your ballast resistor; is the mounting tab on the ceramic case a round shaped tab? If so, it is the wrong ballast and has too high a reistance; DON"T listen to the parts store guys on this item! Higher ballast resistance will starve the coil of current and the spark will be weak and will not fire well, especially in warm-up. The best is to spend the $$ on ebay and buy a NOS Mopar PN 2095501. If you want one faster or cheaper, then buy a BWD RU19 at one of the box auto stores. The right will make a BIG difference in how the stock ignition system will run (wheter it has points or the Mopar ECU system); it gets the spark energy back close to where should be (although not back to the full level of the original ballast). MSD also makes a decent ballast resistor for this; get the one listed at 0.5 or 0.8 ohms cold resistance; that is very close to the original part, which had a 0.5 ot 0.6 ohm cold resistance.

The plug that Pishta lists above should help spark performance in a stock engine.