I've thought about how 'easy' it would be to create a modern urban vehicle in a similar form factor. Actually, you could get pretty close with fiberglass 1926 Model T pieces and parts.
The 1925 Model T roadster had a narrow turtledeck similar to the Milburn. Reproduction parts are reasonably available. It appears that two back halves and four front fenders would provide a close approximation (The T had a square corner at the front of the rear fender). The doors, windows and roof could be wooden construction, or square metal tubes. Reasonably widened and lengthened cabin, 1920s people were thin.
I'd probably go with 19230-31 Model A wire wheels (19") with BMW i3 tires.