The reluctor in our MP distributor already had two grooves machined in it from the factory. DRAM explained to me how to check the phasing, using the hole in cap and timing light trick. It was definitely off on the 383 in our RR. I had removed it to change the pickup coil. I then switched the reluctor to the other slot and it was spot on and the car definitely runs smoother now. The difference was clear, both visually using the timing light and how well the car ran. It was not hard to do, you just need an old distributor cap to sacrifice. It explained the wear on one side of the terminal inside the old distributor cap, instead of the nice even wear shown in the first post.

If you have a MP distributor pull the rotor and look carefully, to see if it has two grooves. If the phasing is off try the other slot before doing anything more elaborate, you might get lucky.