Yes, the template is using the [IMGS_PAIRED] tag to create the paired column of images. For a single image vertical column, replace that tag in the templates with the [IMGS_VERTICAL] tag and store them separate in the template lib (different names) for use. That will provide the same type of standard 400x300 images with the click to Supersize. Try that and check with Preview to see if it's got it correct. I might need to redo the custom overrides if it looks odd.
Hmmmm....I'm curious if that's exactly what you have in mind, as most using single column like the oversized pictures (no click to supersize), and frequently use a split vertical left and right columns, e.g. pictures on left and description on right. Actually, I was experimenting with that look on yours with downsize of the lower banners. That's why that one temporarily shrunk....forgot to reset.
I checked your Store and see you've been very busy listing. Look'in good for PS if that sales rate trend continues.
Danno