At this point, the stub was tacked to the stock frame. Note the gap between the two. Fatman designs their kits for a 1/4-inch gap between the two for a nice weld gap. You can also just make out two of the four back-up plates inside the framerail, which ensure full weld penetration and provide more support than a simple butt weld. These plates were tacked to the stock frame before the stub was slid into place.