So the very first 50BTC is what you are after, what if that person had other BitCoins generated into it since then, how do you know which is which?
I kind of figured that if I had generated the first and only block, the next thing I would do is transfer some coins to another account to see if everything was working. Probably several different times. Then I might try merging them back together to test that too.
It's possible they have all been merged together. That would be a shame for future historians though. If that's true, I might start looking for coins from the first non-tainted (uncirculated block).
Either way, I figure there is at least a 1 and 10 chance that you have the earliest untainted coins. :-)