Here is an unusual A-17783-BR rear bumper arm brace assembly. This is similar to the typical 1928-29 braces except this one also has a factory chamfered relief in both end forgings.
Subsequent research by Marco Tahtaras and Tom Moniz has led to the conclusion that this style brace was used in very early 1930 on coupes, roadsters, and cabriolets prior to the release of the various stamped brace designs.
Per Marco:
"After doing a little looking I found that the new stamped cross brace replaced the tubular brace (on paper) 12/12/29. This would be a bit late as the new '30 models were already in production. "
"With the introduction of the '30 models the bumper arms were shortened slightly. The brace would no longer clear the vertical bracket on Coupes, Roadsters, and Cabriolets as they have the brackets place in the rear most position".
Pictured above is a pic courtesy of Tom Moniz of his 1930 bumper bracket assembly having this late style tubular brace with the notch.