Seems I was wrong again. Got this in a note from Bob MacDonald, where I asked him if his Dad, Rollie, ever built a D-Tube Detroiter. Bob's reply:
"Yes there was one. It was built and published that way because the magazine didn't want give dad enough space to allow explanation of how to build an I-beam. That was the only one and he didn't like it. In fact that year he built two that looked alike one D-tube and one I-beam. They were both painted light blue with dark blue and gold trim."