From an originality stand point, you have to go with a line that looks like the factory original if you're doing a concours resto. From a safety perspective, steel braded line is what is used for most racing applications today. NHRA will not allow the plastic lines and they don't like the copper lines either. I have a copper oil line in my race car and it's broke several times.......much of this relating to what John Z is saying in this thread. I just kept patching it up over the yerars. I will install braded lines in the new race car that I am building this year. Once that is done, there will be no issues to worry about.
That grommet pictured above looks just like the one used in the distributor housing for the wire lead.