Gallery Stack 3 will not process pictures inside a blog list, only in blog details a grid and lightbox will be be displayed, which I hope make sense to you, as this might lead to wrong display of the gallery (where does the lightbox start, where does it end, etc.)
The best is, you create a summery for each blog, with maybe one (or no picture). On opening the details of the blog post, the gallery will be displayed correctly underneath the blog post.
@SteveB: Gallery Stack will take all pictures it will find inside a blog post (details), wherever added inside the HTML content, and display these underneath the original HTML content as nice thumbnail gallery with a clickable lightbox.
I will try to set up a clickable demo on my hosting provider the next days, currently running on MAMP locally without problems