Wow, we have some activity now! Thank you all for your input!
So, the grills are definitely forged, not cast.
The job is on a municipal building, so the "buildup" that everyone sees is simply years of bad maintenance and poor prep under a typical slap of Rustoleum.
I agree that the angled members are not structural. The grilles that I will be reproducing however will be considerably larger, so the joint integrity is fairly important.
I am going to be building 123 of these grilles, so assembling these joints in a timely manner is fairly important as well! That being said I am more about delivering a good product than I am about a profitable one! (not very businesslike, I know)
The "rivets"that hold the scrolls are actually large round head screws! I was thinking maybe I would make a slight taper on the ends of those particular bars and drift those swells with a matching taper instead of straight thru. Then the screw would pull everything tight. The other two intersections of the scrolls are a mystery, however, I agree with Marc 1, I have seen rivets in some of the damnedest places! (and this is a tight one!)
As far as the 3 way joints go, I also agree that craftsmen from this era would only weld something as a last resort. However, this project would have been more industrial and less artistic, and it may well be that brazing is the best option??? I have been doing restoration work for 40+ years now and I don't see a lot of brazing in historical work, but I do see it. I would still have to forge the first pass thru properly, and the fit of the diagonal member would have to be done nicely..........