Overcharging 68Dart...need some short fused help (pun intended:)

Quick question for you guys (and gals) if you have a minute... I haven't gotten back to trouble-shooting this problem, the car is in time out right now while I sort out my thoughts.

I replaced the original (dead) VR with a like VR from NAPA. That's when I started paying attention to the over-voltage condition I have.
After reading posts on the forum, I replaced that VR with a heavier duty Standard VR-106. But, due to the constraints of the mounting location, I moved it from its vertically mounted location on the firewall, to the inner fender mounted horizontally.
So here's the question, would mounting the VR-106 on the horizontal, vice vertical, cause lack of heat dissipation from the resistors mounted on the bottom, and consequently failure of the VR to operate properly?
I'm gonna get back to this in full-force this weekend and work through all the suggestions you've given me.
Thanks to you all for your help thus far!!
-Corey