I have a 70 Roadrunner with the electronic voltage regulator setup. The alternator is a single field, not a double. Is there a way to use this alternator or is that why the voltage output is all over the place? Thanks for any help!  

Yes you must use the dual field alternator with the new style regulator.
If you don't/can't get the dual field alternator then buy the 'modern' 'old style' replacement Wells part # VR706.  

Both the regulator and alternator are new, but since the wiring is all in perfect condition, I will get the dual field alternator. I am assuming that is why it was over-charging as the rpms were increased. Thank you!