What year 389? It makes a difference in how to approach it. '64-older are less desirable heads but good blocks. Later heads DO "fit". 400 parts also fit.
Most important, define a goal for performance/usage. Build accordingly. It's NOT "a Chevy" so most of the "standard" hot-rod modifications made to Chevys don't apply. What car?
Jim Hand's book "How to Build Max-performance Pontiac V8s" published by SA Designs is the most current study of the ol' Injun. It's now 8 years old, sio some of the info is obsolete. The "history", "rationale" and short block sections are ALWAYS "current"... (:-