Ed - they say a picture is worth a thousand words
The main frame (the 83" x 39" rectangle) is constructed this way. Cut the two vertical lengths to 83" and then the five horizontal lengths to 39" minus 2x the gauge of the angle being used. Thus, when welded together, you get the 83" x 39" dimension. Start with the outer four lengths to ensure that the frame is square, then add in the other three.
Next comes the base, which the drawing shows as being 24" This needs to be 24" minus the width of the angle. The reason being is that you can use a butt weld to join this piece to the main frame. The other ends accepts a length of 39" angle (notched as above), which forms the front of the base.
Once you are happy that everything is square, you can stand it upright and weld the two 84+" diagonal lengths into place. These are lap joints and these sit on the outside of the frame. This should be pretty clear from both Ken's drawing (look at the side view) and both of our photos. I'm not really sure how to describe it better.
Next, cut the lengths that divide the rack into three sections and provide support for the shelves. These are easy, as they simply sit beneath the horizontal lengths. On the outside ones, I welded them to both the horizontal and the diagonal. It means they splay out the width of the gauge of angle used (as the diagonal sits outside the frame) but it looks fine and adds rigidity. If you wanted a perfect solution, you would notch the outside pieces, so that vertical side sat flush to the outside of the frame but this is a stock rack and I didn't see the need to be that fussy.
Finally, I added the horizontal lengths to form the front of the shelves, which are welded to both the diagonal lengths and the dividers. These will be slightly longer than 39", as the diagonals sit outside the frame, so measure the width and cut accordingly (they should be 39" + 2x the gauge of the steel being used but just measure it be safe).
As you can see from my picture, I have done this before going back and welding in the inside two dividers. This is because it gives you two points at which to clamp them for welding. The picture shows the top shelf section finished but the others needing completion.
I will get better pictures when I can but this should help in planing yours and it will serve as a reminder to me of what to take pictures of. I'll also give you the lengths of the dividers (will be in mm though).