If you want to get electronic NT texts for free then
you will want to visit:
http://www.znet.com/~broman/editions.html
At this site you will be able to get Tischendorf,
Textus Receptus, Westcott & Hort, NA/UBS etc.
Now you already have Scrivener, Stephanus then you
will not need to get a Textus Receptus.
If you don't have the UBS text, then you have a choice
of formats. NA27 will give you a more complete textual
aparatus. UBS4 will give you a built in dictionary.
Your question on the difference between Scrivener and
UBS would require a long answer to do it justice. If
you have access to a university Library I would
suggest looking up *The Text OF the New Testament by
Bruce Metzger*, 2nd or 3d editions are fine. Metzger
will give a well written history of the different
texts. Metzger is a pleasure to read and I think you
would enjoy it. The book is still in print if you want
to buy it for your library.
Clay Bartholomew
Three Tree Point