Tim I'd just do what you are thinking. If you can't find an original. Fab it out of plate (add a longer bolt and additional spacer of the bed bolt for 2 points to plate.
38-39s brackets bolt up the same way with one through the bed. On 38 it does have two plate mounting points. One over the bed point and one at the bed to plate. You most likely have earlier truck spare tire hardware.
In 36-39 there is a hoop and a locking cap for wide five. You don't have to have it. But just so you know.
Nice book to "pickup"
for these early ford trucks. 1932-1952 Ford trucks, Mack Hils. Not heavy on specifics but good for reference to outer details.
1936 trucks