I don't know if it will work with the HEI or not. Do you know if the tach works? Maybe if you know someone still on points you could test it. Sorry not any help just some thoughts.
.I got a re-pop hood tach and it worked wired straight to the TACH spade on the HEI I have. Don't know how accurate it is. My dash tach and hood tach are 300 RPM different. Not sure which one is right but from the way the engine seems at idle, the hood tach is more believable. But I didn't add the hood tach for accuracy, I added it because they are just total bad ass.