You're much better off staying with a dual master cylinder
set up correctly, making sure the pedal can fully stroke the master. I would not use one smaller than 1", to ensure a full pedal.
Your vintage drum brakes need residual valves, so make sure they are either internal in the master you choose, or inline 10# external.
One serious issue seen in your pictures is the absence of a dust boot that covers the rear, helping keep dirt, moisture and corrosion out of the bore.
As stated, the mounting bracket should be changed, and one like pictured below that bolts to the stock '39-'48 Ford mount is normally used. I buy mine from Chassis Engineering Inc. but they are available from other suppliers or dealers.
Choose a master with a deep push rod bore, (to ensure the rod will not fall out of the bore) if you don't use a retainer on the push rod. All the Ford power brake masters I have worked with or use have deep bores, while the manual masters retain the push rod in a shallower bore. You may find, as I have, that some drum/drum service/replacement masters are a universal disc/drum drum/drum design, with an obvious larger front fluid reservoir, deep push rod bore, and include a bore spacer, push rod with retainer and tube nut adapter(s).