Foundation for the cargo section.
The top tube fits the headset cup. But the headset extension tube is larger in diameter than this tube ... so I cut a piece of 1/2" EMT tubing and split it down one side, cut across to make two pieces, then spread them open to make 1/2-moon pieces to go around and shim the larger tube. This centered the larger tub inside the headset extension tube.
Looking down inside the headset extension tube, you can see the end of the short piece of tubing that the cup fits into.
Looking from the side ... what you can't see are that the shims were even with the top of the headset tube extension, while the inner tube protruded 1/8" above. I then welded the inner tube to the outer tube. And tapped the cup into place. This allows for replacement of the cup and bearings as they wear.
This is the extended tubing for the headset.
It was cut, and a 3/4" EMT tubing was welded in between the two pieces.
If you can differentiate it from the parts in the background ...
There's the frame temporarily on wheels.
Another view from a rearward angle.
Gotta work on steering rod and brakes next.