Tony:
Here's another thread...I believe they are stamped steel, fwiw.
Dunlop Wheels?
I believe they were used as a more robust alternative to the wire wheels on the early cars although many other cars of the period competed with wire wheels...the later halibrands, kidneys, fia's, were more of a region-specific solution for robustness and increasing tire width requirements..
Somebody please correct me if I'm off base..
- Allen.