I am trying to install on a Rocket Theme template (advanced SEO URL) and do not have the following:

styles/prosilver/template/attachment.html
styles/prosilver/template/posting_editor.html
styles/prosilver/template/simple_header.html
styles/prosilver/template/forum_fri.js

Will this mod still work, anyone know what I need to do?

The style may be based on subsilver2, have you tried the subsilver2 code change, they may better fit into your style.

I just did a Mod job on a rocket theme site with phpbb-seo and works fine.
if you do the code changes in the prosilver and subsilver styles then the rocket theme will use them.
There is missing files because the theme uses the new Template Inheritance.

mitch wrote:There is missing files because the theme uses the new Template Inheritance.

Just in case, when style Inherits from other template, you need to make sure that the Inherited template are modded as well.
Since Inheritance should be done from prosilver or subsilver2, you need to make sure that the two default styles are up to date and modded too