IBM documentation is the best I've seen during my entire career (30+ years).
I agree with you, IBM Redbooks are excellent. I mentioned the Design Guide to several folks and even as a starting point, it's quite good.
I still see it as an ambition of mine to get the opportunity to be involved in the authoring of a redbook.
IBM don't exactly do search very well on any of their websites.
I'm sure you already knew that. Just putting it here for anyone else that may come along and read this.