I high lifted my door for a 4-post lift and the garage door company recommended i-Drive. I would strongly recommend against i-drive.
It was torsion spring in tube balanced but it didn't matter. It would not hold it's set point, couldn't be fixed by the installer, and was replaced twice before the garage door company finally offered me full credit toward a Chamberlin Liftmaster jackshaft type opener. -I do have to give them credit for standing behind their install.
The liftmaster mounts outboard, direct coupled to the torsion shaft, above door height and to the side. Nice package, about 18" tall, 8" wide, 8" deep.
Very quiet, very smooth, and after about a year, no problems.
http://www.liftmaster.com/cons...ail.aspx?modelId=834Kelly