Two of the major manuscript lines are the Alexandrian and the Byzantine. From what I recall, the Alexandrian family of manuscripts tends to be more polished than the Byzantine family. Tony had commented how one professor preferred the Byzantine majority text. Part of the reason, I would imagine, is the "less polished" nature of the Byzantine family. Here is how Revelation 13:18 is preserved in these two families (taken from the Parallel Greek New Testament Website):
wde h sofia estin o ecwn noun yhfisatw ton ariqmon tou qhriou ariqmoV gar anqrwpou estin [kai] o ariqmoV autou [estin] cxs
wde h sofia estin o ecwn noun yhfisatw ton ariqmon tou qhriou ariqmoV gar anqrwpou estin kai o ariqmoV autou exakosioi exhkonta ex
The number 666 is written differently in these two manuscript families.
exakosioi exhkonta ex
The Byzantine follows the ancient Greek way of writing numbers (cxs -- where c is the letter for 600, x is the letter for 60, and s is letter for 6), as I wrote about in a previous blog entry. The Alexandrian family writes the number in a long form, exakosioi exhkonta ex, where exakosioi literally means 6-hundreds, exhkonta literally means 6-tens, and ex is 6.
So, what are we to make out of all this? The road has a lot of interesting twists and turns.
There is one interesting theory on the variation of 666 with the number 616 that I read from Beale. If the scribe was working with a "Byzantine" manuscript with the number written as cxs, the central "digit" x (ksi) could have been written sloppily in the manuscript the scribe was copying from, it could have looked straight to him, like i (iota). The scribe would write cis in his copy, which is literally 616.
Tony offers a fascinating theory for 666 in the comments of my previous blog entry. Read it and see if it makes sense to you. I offer some theories in my original posting on the topic. Depending on how the number was written in the original manuscript John wrote, some of the theories would make more sense than others.