If you find it hard to keep track of what tpl file is used for what forum part or page there’s a simple way to keep track of it. Open every tpl file and add an HTML comment containing its filename at the top and the bottom of it. So if you edit viewtopic_body.tpl you would add the comment <!-- start of viewtopic_body.tpl --> at the top, and <!-- end of viewtopic_body.tpl --> at the end of the file after all the other HTML and template code.