according to my hollander, the rear leafs are interchangeable. they are : 1 3/4[w] x 24 13/16c.28 13/16
they fit :dodge 35-52,desoto 49-52[except8 cyl,8pass], plymouth 37-52,chrysler 49-50, 50-52 windsor & newyorker, and imperial 50-52 except crown.
the fuel tanks show only 49-52 models chrysler,dodge,desoto, plymouth interchange, but it's possible they are very close to the 40 model year,maybe needing very slight mods to fit up.
hope this helps.