[Boog]

Yes the coil integrated larger diameter dist cap was the identifier for an HEI (high energy ignition) system from the beginning but somewhere around the early 90's GM separated the coil and cap again but still retained the hall effect, coil pickup design. It has been my assumption that this system is still HEI since it is of the electronic ignition design. I also assumed GM removed the coil from the cap in order to use a smaller diameter dist for under hood space concerns.
The product listings @ RockAuto and O'Reillys is the confusing part.
The images of those ICM's are the same and the product specs are the same but one says HEI and the other says non HEI. As far as I know there was only one ignition system used on these 88-98 trucks. And all those listed say they do fit a '91 Chevy truck. I'm just looking for some clarification on these parts. Thanks