You can also say ならともかく which has the same meaning.
ex#5780 ものではない means : " shouldn't". So,I feel that it may be わけがない (impossible, by no means) or ことができない
>誠 Thanks for your great contributions to this site! Yes you are correct that わけがない and ことができない are good translations for "by no means"/"impossible". However, this example uses "読める" which is like saying "できるものではない" rather than just "ものではない". Therefore I stand by my translation.
You can also put 「は」 or 「だったら」 before 「いざしらず」, not only 「なら」.