OK, I found some pictures of the second frame I built, using NRS fittings but a combination of NRS and locally purchased pipe. You can see the standard NRS yoke on the other end of this frame (one of two halves for my 20' tubes. I also added a picture of how the fabricated jackass mount fits in over the home-made yoke..
I did this because I wanted to be able to do some things that the NRS welded yoke -- with its drop in the center -- wouldn't allow. So I took NRS fittings and conjured up my own yokes.
As it turns out, this version has the same drop as the standard NRS yoke -- that is, the floor attached to this is at the same level as a floor in a regular NRS cat. But the bottom tube of the yoke's crosspiece is level instead of raised, and the top tube is level with all the other crossbars on the frame.
The beauty of this is that if I decided to go with a lower or higher floor, I could achieve that by substituting just four short pieces of vertical pipe, and get any amount of drop I wanted.