Carl,
You may want to think about using the setup I did. I had a hitch receiver welded on extra strong. Then I bought tubing from Northern
Buyers 48in. Long 2in. Standard Receiver Tube | Hitch Receivers | Northern Tool + Equipment
They sell it up to 48 inch lengths. This is the 2-1/2 inch tube. You can then buy the inner tubing which can plug into this for extra length if you like. I had the receiver welded with fins to reinforce the tube.
It's plenty strong. I can lift my tractor up off of the ground without any problem.Your larger attachment plate would offer more support than mine. You could weld on even wider fin's along with maybe a 3 or 4 foot top strap, using flat steel for more reinforcement.
Just a suggestion. I went with this setup so I can also make a rake plus other attachments, winch etc. When I get er done. I should have added another 10 plug in attachments to my list. Here is the plate once again and the outer tubing just in case you're interested.

By the way nice job on the rake.