You should probably search the forum with different search terms - I believe I've seen this topic a few times here over the years.
You may be able to do it without needing the Muscle seat but it would probably not look/fit cleanly with other HD stock seats. The Muscle seat has a portion that is bolted to the fender and the other part flips up to access the fuel tank. The other tricky component would be the LED tail light / turn signal unit. I doubt it would plug right in to the Night Rod's non-LED setup.
I'd say: Muscle seat & fender and a way to make the lights work.
It may be easier to start with the Muscle and change other parts to move towards the Night Rod...