Ah, OK.
A friend of mine had a unique take for the role: Michael Jai White. The guy who played Spawn.
His thought was, back in those days, a black man would probably be the one chosen to test such a serum, just in case of failure. Then, they could have the spy aspect of Cap played up, with the US dissavowing knowlege of him because of relations with blacks at the time. FFWD to the future, after being frozen, and how the more Politically Correct world embraces him.