If they really wanted to do the whole 1950s ufo roswell thing they could have had the Russians believing what they were looking for was alien (some kind of artifact but not a lame plastic skull) but it turned out to be something else. Indy even said himself "Oh, c'mon! Saucer men from mars?!" I was really hoping the area 51/roswell angle would be a red herring and it would turn out to be something else that actually fitted into an indiana jones film but then they showed the alien corpse with it's head cut open in the tent and it was all over for me.