My newest story idea features a rather long part (probably a third of a novel-length work) in which the protagonist confronts the antagonist in regards to a discovery about who the antagonist really is. This leads to a story within the story, which is akin to a long flashback (think Interview with the Vampire where Lestat is recounting his history to Danny). One of the things I disliked about that particular example were the constant quotes-within-quotes where the character is recalling dialogue. The only option I can think of is to have the book in three parts, where this particular part (the second one) would switch from third person to first person. Is this generally acceptable or is it likely to cause a whiplash thing?