1939 is a bit before my ability to comment from hands-on experience. The late 40's and early 50's spindles, etc. would accept conversion to Bendix type brakes, but it was necessary to use everything from the backing plates out- - - -backing plates, wheel cylinders, shoes, hardware, hubs, drums and all. Someone a little more experienced with the pre-WW II brake systems and spindles will need to offer some advice about the Bendix brake conversion. It would be an excellent idea, if it's possible without a great deal of modification.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!