Low voltage at the ignition can be a real problem. I assume by your issues you're running a 1 wire alternator, I suggest switching back to a 3 wire style, like a 12si or more modern cs130.
This article convinced me it was the way to go. I had all kinds of charging and voltage issues on a one wire alternator back when I had a 72 cutlass, at idle it could barely power the lights, and I'm pretty sure it was the cause of some of my off-idle stumbling issues.
http://www.madelectrical.com/electri...hreewire.shtml