First, the convertible/station wagon is different than all other models. The 39 convertible dash is about 1" shorter on the sides than the 1940, so to install you have to shorten the innner mounting brackets slightly (to go the other way just shim).
The Coupe/Sedan dashes appear to be about the same height 39/40 so the only issues I can think of are steering column mounts and dealing with the windshield swing out hole.