All 1939 Fords had hydraulic brakes. They are the same as 1940. Should be interchangeable parts.
Assume you are wanting to go from the wide-5 to the 5 x 5 1/2 inch rims? Should just have to change out the drums and/or hubs and drums. If the drums are swaged to your current hubs, then you will have to cut the swaged area out with something like a thin hole saw. Or if you can get the hubs and drums just switch them out.
Wide 5 hubs and 5-1/2" hubs are totally different; you can't mix drums between the two.