How to Move User avatar in River feed to bottom?

I am attempting to make a plugin for elgg that will reorder the river stream.  Instead of the user avatar being the first thing to appear, with the post title to the right and the tags and posted on date followed by the summary, I would like the post title to be by itself at the top, followed by the summary, then the user avatar and the tags/posted on date to be at the bottom. Where is this stored in the core to know how to override it?

I know you are not supposed to edit the core, and I won't, at least not on a live site, but I would like to know where the river layout is stored so I can rearrange it in a new layout plug in.

Any help is appreciated and you guys are always very helpful.  Thank you so much in advance! One day I hope to be able to answer elgg questions in the manner that many of you do.