i downloaded a pack with a shit ton of crop bars. Its just a png file that i drop on the track above my video clips. That way I can adjust the clip and the widescreen mask is not affected at all.
As far as exporting. Don't ask me why i do it like this but i do.
Heath my export settings would actually work for you because they are 1080.
not sure if any of that helps. I learned from a ton of trial and eror so it's hard to put into words haha