Car dropped 250 RPM and is now stuttering

Did you go back and plug the vacuum line to the distributor vacuum advance and check the advance at 2200 RPM, as well as at idle?

Your battery and electrical system voltages look normal. Now just check one more spot: voltage into the MSD unit.

Set the engine at TDC and remove the distributor cap, and make sure the rotor is pointing directly at either #1 or #6 spark tower. Look under the cap and at the rotor carefully for any odd appearance.

Use a vacuum gauge and look at the vacuum in the intake manifold at 'idle'.