If I could ever get more than an hour or two at a time to work on this, I'd be making much more progress on it. That said...it became much more "bench looking" today.
Got the 3 cross pieces welded in today, everything is square, true, and solid as a rock. I don't think there is any need for any diagonal braces on this...plenty stout as is.
The top isn't attached yet, just sitting there for now.
I'm weighing options now about how to attach the top, whether a front to back cross brace is needed to secure center of top, whether to strip the scale off the top side or leave it...etc etc.
Next time in the shop I'll drill the holes in the bottom of the pieces that will go left to right that the side extensions will slide into then get them welded in. I'll weld nuts over the holes that will let me run a bolt in to clamp the extensions in place. Easier to drill them on drill press before attaching the tubes to the frame.