This is a handout Jim Boyce provides his Greek students. It differentiates internal and external evidence for what reading of a particular text is the oldest and best. 
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www2.luthersem.edu
Dr. Ciampa teaches at Gordon-Conwell Seminary. I don't know him personally but have corresponded with him around permission to send you to his materials. They are well-organized and clear. 
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www.viceregency.com