That's about it, but I mentioned early in the thread "Six bolt wheels required because of the GM truck rear end swap, in the spirit of how it might have been built in the pre-Ford 9" days. Front hubs would be drilled to match so as to only carry one type of spare wheel".
Just FYI, GM truck rear ends were used in lotsa stuff pre-'57 when the Ford 9" and the equally tough new Olds and Pontiac rear ends were introduced, where ultimate strength was more important than unsprung weight. The original SWC Willys coupe is the first example that comes to mind.
While unsprung weight would be an important consideration for running on rough roads at 50MPH+, the ultimate strength of the axles themselves, and the wheels, might take precedence...depending on the preparation philosophy of the particular car builder. Race-car prep is always about compromise and tradeoffs.