From Mike Gartland:
I’ve seen the originals to Suspense 39 and there are no Kirby margin notes. With this particular instance you have a Kirby concept that was pitched to Lee, the cover to Suspense 39 might actually be the Heck-inked concept drawing, who knows! Since we have Heck confirming that Kirby designed the character (Heck states that he designed the look for Stark and drew all the art for the story) we can be safe in our assumption that Kirby created the look of Iron-Man; but since Lee/Lieber/Heck did the story/art (there are no Kirby layouts here) we have no way of knowing how much of Kirby’s ideas for the character were used. So this character may honestly be a co-creation, so far there simply isn’t enough evidence to suggest otherwise!