One quick comment in favor of the fUSSR having a chance to be very good at American football:
Anybody who things that the US (or other countries with large black populations) have the market cornered on amazingly fast/high jumping athletes hasn't been to Scandinavia or the Balkans (or Russia, for that matter). There, white kids aren't brought up being told that they can't jump as high, run as fast, etc. Did the USSR produce many modern sprint champions? No. BUT, no team sport athlete is a TRUE sprinter (and neither Vick nor Moss would be that great of sprinter, anyway). Remember (or learn, if you didn't already know), life is a bell shaped curve, Americans see the outliers (WC-class sprinters) and assume 'all blacks are faster', when this is simply not the case. How many kids have been 'converted' to endurance athletes by hypercompetitive parents having them work 20+ hours a week at running, hs team practice, club practice, etc?
That said, I still think we would always win, for the same reason that we would have won an all-out war with them (assuming that our idiot leaders didn't go nuclear): Americans simply have a will to win and the ability to be creative in adversity. That is, fundamentally, why I think the Soviets did so well in linear sports, but never got great at team sports (except volleyball, which is still pretty linear).