I just finished installing an HEI distributor in my 68 C20 with a 396. Started with a used GM HEI and installed the Petronix Flamethrower (Multi Spark) tune up kit in it.
https://pertronix.com/pertronix-d800...l#.XWzCkyhKh9M
It is working well and very happy with the install. If you don't have access to a GM HEI they also sell complete distributors.
https://pertronix.com/stocklookbydis...Chevrolet#auto