Could you print small copies of his movie posters on edible paper, make frames for them and put them around a cake with maybe a cowboy hat and boots topper? Jeri C. did a great western wedding cake with lots of good ideas.
I do some western theme cakes and make the dark chocolate fondant look like tooled leather... you could use that same idea with some cowboy boots, wagon wheels, and of course it would not be John Wayne without his guns!