Ah I just found something that might be most (if not all) of the cause of this- my tach is apparently taking a dump on me. I was just out working on the car and I noticed that the tach suddenly and momentarily jumped up to over 1200 rpm - but the engine didn't though. I thought I just had a bad connection so I checked the coil and power connections and figured that was the problem, but a few minutes later it did it again.

So either my tach is dying on me or my Pertronix is. I tend to believe that it's the tach since the engine didn't vary it's speed not one bit when the tach acted up. So it looks like I might be in the market for a tach. Any suggestions for a readily-available points/dwell/tach (digital or analog) that plays well with both points and electronic systems?