Escutcheon, interior door handle ($12)

An ESCUTCHEON for the base of the INSIDE DOOR HANDLE for cars from the late 1920's
Fits Marmon: Model 78, Model L, Little Marmon, Big 8??

The Handle into this Escutcheon for the interior door with a 5/8" retaining ring.
The escutcheon then screws into a one inch thread built into the door.

These might have been purchased by Marmon from an outside vendor that also sold them to other auto manufacturers.  If they look like yours, buy the plastic samples and see if they fit.  If you like them, purchase the steel versions.

The original mechanism was made from pot metal and swelled with age. 
The handles were often held onto the escutcheons by peening over the soft metal of the handle so that it folded over the edge of the escutcheon.  When the pot metal swelled, the handle locked up.

These redesigned assemblies are held together with common retaining rings, making them easy to take apart to clean and lubricate in the future.
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Buy the plastic version to test for fit before comitting to the expense of the steel version.
If you are low on cash and NEED a handle, you can just paint the plastic parts and see how long they will last.
With gentle use, they may last a while, but if you have the money, get the steel.
I do not think that the plastic version would be strong enough for regular use by your passengers.
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