You can edit .po files in text editor. Structure is very simple (some header, do not touch it) and a number of translations like that:
#: 404.php:21
msgid "Sorry! Page Not Found !"
msgstr ""
You can ignore comments started with #.
msgid – string how it appears in php code
msgstr – translation (if empty, msgid string will be shown on site)
You can find and simply copy 60 sets of 3 strings each from English .po to your-language .po by text editor. Then open poeditor and tranlate new 60 strings, or even simply do this job in text editor. You will need poedit only to create a new .mo from your .po file.