As a 'side note' I would like to caution all that when using the 'Green Bible' to look up parts for your '40, you must keep in mind that the parts listed within that book are service replacement parts and while they certainly would fit and function properly, there is a great chance they would not be identical to what was factory installed upon your vehicle. Also, using a 1938 parts book is (obviously) useless to find 1940 parts
Anyway, hopefully, this will aid you Mr. Means as well as others...
There was but one bracket utilized for the 1940 Ford convertible spare tire hold down. It was painted (dipped) gloss black. A special bolt & nut was used with this bracket. The 'foot' of the bolt was placed within a sheet metal loop spot welded to the trunk floor. Holding the bolt within that loop was a plain steel cotter key.
I have included a photo of a NOS spare tire clamp.
Fordially,
Mike "Kube" Kubarth