Hi everyone, these are the responses received from my request for materials for patrons with Alzheimer's. Thank you to all who responded.

1) Veterinary books by James Herriot.  Each chapter is the equivalent of a short story.  They are available on MeL in Large Print.

2) Short story collections worked for a while - mostly in the genres he liked before.  After it progressed, trivia books/factoid books/bathroom reading books seemed to work really well - the shorter, punchier text was easy to comprehend and would often trigger other memories.  Your patron might also like some of the juvenile/YA science books - they tend to have large, colorful illustrations, simplified text, and be relatively short on each topic.

3) Collections by Dave Barry, Erma Bombeck, O.Henry, James Herriot, Tom Bodett, and Garrison Keillor might be possibilities.  David Isay's StoryCorps Project books might be of interest too, but I think they're less likely to be in large print. 

4) Reader's Digest Large Print magazine

5) Check with your area literacy council or program.  Ours has novels that are condensed into smaller books.

6) Try books with one or two characters. That seems to be one way to make the story easier to follow.