(About his birth date)
Bill: Richard Bozulich gives 29 May 1829 http://shinbo.free.fr/TheMagicOfGo/index.php?tmog=21
 (About his death date)
All sources agree about the Japanese date 1862-VIII-10 (that is, 文久2年8月10日). However, that date corresponds to 1862-09-03.
 (About score)
John F.: It was a 2-point margin, though this was not discovered till recently. The traditional accounts are marked B+3.
 (About his strength)
Harpreet: I'm not trying to start a fight, really, but to what degree do people here feel that Shusaku has been overrated? Never mind that he had an ancient spirit playing his games for him [fictionally, c.f. Sai in Hikaru no Go], he still was not able to best Honinbo Shuwa. It seems to me that at least some of his winning percentage comes from the fact that he was a bit of a sandbagger for quite some time. He was not promoted quickly enough to reflect his strength and so he unfairly had to play as Black more than he should have.
Yes, they're all dead now but I feel a little badly for Shuwa who seems to have been stronger than Shusaku. Also I feel badly for Shuho who just had a lot of bad luck in his life. The jubango against Shuho (who took all Black) was lost by Shusaku. That's not domination, just unfair overshadowing.
Dieter: I don't know about the Shuwa-Shusaku statistics but I do remember having read that at some point Shusaku would move to White, which was refused. Also, even if he occasionally found a tough opponent (such as Ota Yuzo), he still was the best player overall.
Andre Engels: Yes, he would move to White, but that would still be only at sen-ai-sen, that is, Shusaku would have played as Black in 1 out of every 3 games. He clearly was able to score much better than 50 percent with Black, but we don't know what he would have done as White. Invincible contains a list of all known games between the two. In the 17-game series (1846-1847), Shusaku scored 13 wins, 4 losses, of the games after that (1849-1851, plus one suspended in 1860) he came to 3 wins, 1 loss, 2 games unfinished. All of these were played with Shusaku as Black.
Hyperpape If he's winning 76% of the time with Black, and then moves to sen-ai-sen, that already gives him a (slightly) better than 50-50 winning rate. So if he can win a decent fraction of his games as White, that's enough to promote to even over a long series. There would be some interesting room for a statistical analysis here, comparing winning rates as White and Black for different players. A post by John Fairbairn at L19 is relevant here: http://lifein19x19.com/forum/viewtopic.php?p=46359#p46359. He notes that Shusaku won just over 50% as White, though presumably Shuwa could hold him to a bit less.
Spirit: I agree with you Harpreet. The commentary in Invincible also heavily favours Shusaku over other players and it's almost the only book on go history available in English, so it's nigh on impossible to get a fair perspective on things. If I read some other background material though it's mentioned time and again that Shusaku's reputation is overrated in the West. Personally I'd love to know more about Shuwa and Shuei but information is almost impossibly sparse on both. It really is a pity.
Anonymous: It is also stated in Appreciating Famous Games that Shusaku refused, out of politeness, to move up against his master, so that if Shuwa lost, he could always have the excuse of playing white. Therefore, it is not known for sure which of the two was stronger.
Zengarden Mention should also be made of, Invincible, John Power's classic biography of Shusaku with deeply annotated games and a wealth of information about both his life and competitive go conditions during his times. The book, published by Kiseido in 1982 is still widely available, and is in my opinion the finest Go book written in English.