My understanding, Snowdog, is that the first section, up to the point where a character dies (not wanting to give too much away), was pure Zelazny, the rest wasn't. Though I could be wrong.
I've researched this point, and others, for the annotated Zelazny story collection and biography forthcoming from NESFA. The bottom line is that you're probably wrong, and it is not possible to pinpoint a particular section of the novel where Jane Lindskold took over.
The reasons for my conclusion are:
1) Zelazny's handwritten outline of the novel goes way beyond the point that you mentioned because the beloved character of Donnerjack Sr was not the focus of the planned trilogy - the *son* was the title character, not the father.
2) Zelazny's own handwritten, complete sections of the novel span parts beyond the point that you mention.
3) William Sanders, an author well acquainted with both Zelazny and Lindskold, and who apparently saw close-up how the completion of the novel evolved, wrote in an essay "Jane boldly disassembled Roger's beginning chapters and rearranged the whole structure of the novel. This is another reason it is so hard to tell who wrote what; Roger's original text is not printed as an integral whole, but is distributed in hunks and chunks through the present book. More boldly still, she completely rewrote certain parts, and threw out bits that didn't work. She acted, that is, as a genuine collaborator, not just a posthumous amanuensis—which was exactly what Roger had asked her to do."
It is true that Zelazny's contribution is about one-third of the final novel, but that doesn't mean the first third of the novel, it means about one-third of the material. Most of that material is in the first half of the book. But all of the first third is not entirely Zelazny's work.
As part of researching the biography, I have had the privilege of asking Jane Lindskold many questions about Zelazny and his work, but with respect to the question of exactly where she "took over" the writing, she has wisely declined to answer other people who asked (some of whom were apparently quite rude in how they asked, and angered that she wouldn't), and I chose not to ask this one because I don't think it is really answerable anyway, as Sanders' essay made clear.
Chris
