Best to ask a good tire shop but I suspect it would be the 205/70-14.

I can't say from experience because the '68s went to the F70-14s. Over the years I ran several different 14" sizes and styles (white, red, raised letter, and even snow tires) as tires evolved.
Personally, mine came from the factory with WSW rayon radials but, despite my quest for originality, now run the Coker repro redlines because I like the look on by car. I rationalize it by the fact that redlines were a '68 factory tire, just not "as built" on mine.