Here is the bolt line on my HD bucket. Look correctly located?View attachment 329190
My bucket is the HD per dealer. He showed me the std duty and it had no holes at all. Additionally, the HD bucket is grapple compatible and it has 2 holes, 1 each side on the top and rear corners thru which the grapple pins and rotates. I compared the std duty to HD and mine had these 2 features which led me to believe it was HD. The Deere website even says the HD bucket is the only one for 553 that is compatible with bolt on edge and grapple. They may have changed some bucket features?
The simple cure might be to drill new holes in the welded cutting edge with a 5/8" hole saw or torch them in. The new grader blade should have the slightly squared shoulders for the plow bolts to lock them down. I would space these holes two inches from the leading edge on the welded in place blade. Pretty easy job with a torch, takes about an hour with a hole saw and drill.
I don't have my tractor at my house but the welded edge is 6 inches wide from back 90 degree edge to front of tapered edge. From the picture it looks like the taper is about 1 inch of the 6 inch width. There is probably 1 inch of width not underneath side that is the overlap to allow the weld. So there is probably 4 inches visible in the picture that is not tapered . The edges are apparently dependent on the carrier type as well. Since I have the global carrier I had the get HD bucket for bolted edge and grapple compatibility