I would wait to see the letter. It seems unlikely that American Express would even accept copies you made yourself. See this thread (beginning at post 217) for discussion of difference between IRS forms 4506T and 4506:
http://www.flyertalk.com/forum/14306726-post217.html
They've only ever asked me for the first 5 pages of tax returns for the previous two years, and never for a 4506T. YMMV (or MMMV as the case may be).