here's some pics of an original trunk tool box for the coupes and roadsters. hope the dimensions are clear enough to figger it out the curve at the end is about the same as a roll of masking tape. the two mounting screws on the side have the same threaded inserts like the seat wood, and the bottom sits on a scrap of the same light canvas they used on the roof. note the small relief for a fender bolt, about as round as a 50 cent piece. the goofy fit at the curved end is the way ford did it. the guy didnt care that day or what? all the material is 1/2" thick, good luck!
in review, i see the dimension for the low end of the back near the curve, got cut out of the photo, its 1 1/4"
hey rich, i've seen those before. while the sure would be handy, they dont have much of a "look" to them!