This is extremely awkward English; the literal translation does not work. Here the conditional is implied, and the translation is "I wouldn't say it either." This kind of thing is subtle but important, as it distinguishes someone who knows English from someone who is translating it literally. AND the "lo" here refers to the thing said rather than the person it is said to, the d.o. rather than the i.o. as commented previously in this discussion.
In English you would never say "either I" or "neither I," that is, neither would come before the subject. Very different from Italian. But when you say "neanch'io" could it mean "not even I?" as in "Not even I would say that? I do think either way that the conditional is implied in English.
"Neither you Simon, nor the fifty thousand Nor the Romans, nor the Jews Nor Judas, nor the twelve Nor the priests, nor the scribes Nor doomed Jerusalem itself Understand what power is Understand what glory is Understand at all Understand at all" http://www.lyricsdepot.com/jesus-christ-superstar/simon-zealote-poor-jerusalem.html