After you do all you can to shrink the wonky areas to assume as much "straight" as they will, I would long arm it block by block. I definitely would not use a pattern that went outside of the block. I would do each sashing by itself. That way the quilting patterns would be complete within each block and within each set of sashings. If you do anything like feathers or vines or fans, etc that wander over the whole quilt it will only accent the lack of preciseness. By keeping each block and sashing seperate no one will notice that the connections between them are less than quilt police perfect. Each block and sashing will be a unit of perfection set next to another unit of perfection.