Misfiring / stuttering issue

Hi guys,

I'm having a strange issue since I installed an MSD Blaster 2 coil, new plugs and wires. Sometimes the car will stutter, as if it had lost spark, and I can't pinpoint why.

This is what I have of info for you mopar detectives:

Currently Points distributor, will install a pertronix conversion kit soon.
Coil installed through ballast resistor. On idle ballast reads, 10.5v in, 7.5v out. Under throttle at 3k rpm, ballast out is nearly 12v (???). Ballast problem?
Plugs are set at .0035 as per factory
Plug wires are 8.8mm good quality stuff

Today I noticed this:
Drove the car in town for about 30mins. Stopped by the side of the road, car idled ok for about 2 minutes, then stuttered until it nearly stopped, then regained idle.

A few minutes later, while going through a roundabout at low rpm, it happened again. I increased rpm, problem went away.

It feels like it happens at low rpm, but I can't be completely sure. Maybe a problem with my very old charging system? The alternator only puts out proper charging past 1,500rpm.

I even thought it could be dirty fuel, but I keep thinking if that was the case then it should be happening more often.

How's this for a puzzle wrapped on an enigma?

Cheers fellas!