Hi @tophermurphy
We’ve added a link to v3 docs in the top bar, thank you for the feedback. 
We can’t have the v4 docs search bar to search for v3 docs, and vice-versa, though. These are 2 different search indexes that are separately handled by Algolia.
Some guides were removed from v4 docs as either they are not up-to-date (they’re under rework) or what they cover is now part of the v4 core features.