Combined right and left columns possible?

you don't have to combine the right and the left sidebar, when looking at your "blocks" menu make everything go to one side, either left or right. And if you don't want left or right in 4.7 now you can but blocks in the header or footer.

I might have figured out what you want. Open up the page,tpl.php in an editor like dreamweaver. And you have to hack up just the positions of <div><?php print $header ?></div> and move it in a div that is not inside the div that contains the left/right and center content. So if looking at the bluemarine tpl just put the div or a new table with <div><?php print $header ?></div> outside the existing table (note: erase the original <div><?php print $header ?></div> from the tpl). now you got the placement you want.

HeaderHeader
HeaderHeader
L          R
L          R
L          R
L          R
L          R

To finish it of you need to use css the postion the blocks inside the header correctly

If you don't understand what I said, search for theme related stuff not php snippets.