The Bible text is the so-called pure Cambridge text, and is based on the "Allen 127 ASCII Text Format" file from the site bibleprotector.com. The pronunciation marks were added based on The Oxford self-pronouncing Bible published in 1897. For reference you can get the final source Bible text here. That file is designed for internal use and not for direct reading, but all scripture on this site uses that text as its starting point.
You can get the Bible Protector text file here, and a scan of an original printed 1897 Bible can be viewed or downloaded from the site archive.org here. Please use the Contact page if you find any differences between those files and the text you see on BibleStudy.tools.