I presently have a Dick's Welding Extension, that is rated at 450 bushels. It is square and it is roughly a foot higher than stock extension and flared out and no up right, but can put flip ups on all sides to increase capacity. I presently purchased this extension for $1300, with bubble up auger and installed. These are made in Windom Minnesota. The number is 507-832-5650. If I am not mistaken, I think mine is measured 13.8 without bubble up auger. I will get you a picture of my combine if you would like to see it.