Nash,
There is some confusion here. Let's clear it up a little. GM didn't start using HEI until the mid 70's. Accel makes an HEI and they also make an HEI Super Coil. Your car came with a points distributor. Not to be confused with an HEI. If you have an Accel Supercoil it's probably on top of either a GM HEI or an Accel HEI. If you have a 30+year old distributor it's not an HEI. You could have an Accel Super Stock Street Coil attached to your original points distributor.
An HEI is one of the simplest ways to improve over the stock distributor. After GM came out with them in the mid seventies it was the best thing going for a quick swap. Accel came out with the Supercoil that sits on top of the GM HEI in the 80's. Now, twenty some years later, most of the GM HEI's are all worn out too. Accel came out with a high breed HEI a few years(maybe 10)back. It's an amazing unit that as a electonic board in it where the GM had solid state electronic parts. I bought my modern Accel HEI from Summit. I'm happy with it.