AM, you are correct that 607 is Gregorian and not Jewish Calendar and 2520 figures in both calendars resulting in 1914 in Gregorian years but the 2520 in the Jewish calendar as you pointed out, also corresponds with 1914.
I do not know for sure if 607 is correct but it makes sense to me: 539-70 = 609. So, if the 70 years began after the assasination of king Zedekiah and if the Jews did stay in Babylon for 70 years, 607 is at the very least, plausible, based on the Bible.