Here is a non-elegant solution for suppressing the header and/or footer on the Atahualpa theme that I came up:
For the header:
Go to Appearance / Editor
Select Header.php
Find <!-- Header -->
Insert <?php if( !is_page('2548') ) :?>
Find <!-- / Header --> (about 5 lines below <!-- Header -->
Insert <?php endif;?>
Click Update File
That's it. In my case above, I wanted the header on all pages EXCEPT page 2548. Choose your page id accordingly.
The same new lines work for the footer.php file too if you don't want the footer on your page.
For the footer:
Go to Appearance / Editor
Select Footer.php
Find <!-- Footer -->
Insert <?php if( !is_page('2548') ) :?>
Find <?php wp_footer(); ?> (about 16 lines below <!-- Footer -->
Insert <?php endif;?>
Click Update File
I figured out the above from a hodge podge of stuff I found regarding generic Wordpress. I am not a coder - so there may be a lot better way to do this.
I personally find this way to be a pain in the ass since every time I want to add a new sales letter without a header, I have to manually go in and edit the header.php file and add the new page ID - but at least this works.
I would love to see a future version of this great theme include a blank page template choice that would do all of this as easy as a drop down menu. There are a LOT of folks who do sales pages who could use this.
Hope this helps anyone else looking for a workaround for a sales page for the Atahualpa theme.
If anyone has a more elegant solution, I would love to see it!
Robert