Upgrading to electronic ignition help

I have no idea what a "firecore" distributor is

You didn't say, but a wild guess, from your name, is this is for a slant? or whut?

The problem with "rebuilts" is that you don't know what you are getting, I don't care WHAT the application / catalog said. Most / all will have a 70's "smog" advance--not the best for performance. That is, "figgure" on recurving the dist. or at least finding some lighter springs