Here's an example of one of my ended auctions with 16 Thumbnails, using the standard Auctiva template and Thumbnail group.
View: Hemingway First 49 Stories
Note, the large picture changes as you hover the cursor over each Thumbnail, or you can click to super enlarge (best of both capabilities).
To do 40, it probably makes sense to do some custom HTML coding, using that grouping and code as a template guide.
Danno