Are there any aerial maps of Delacroix Island Louisiana from the 1940 to 1990?

The best thing you could do is contact USGS about arial photos. You can go here

http://Louisiana.hometownlocator.com/maps/feature-map,ftc,1,fid,560618,n,delacroix%20island.cfm

and scroll down to the map, then click "satellite" or "doc" on the map and see real satellite photos, but you must contact these companies for earlier photos, but yeah, they've got 'em.

Take a bong hit and write out a good letter to them. Be nice and give them a good reason to let you access the photos.