Its me again lol

Post #20 [ my post makes 1000000% sense ] in conjunction with post #13 that I linked to it. That course of action [ more idle timing] does get the idle speed down [ slightly ] & also gets the most efficient idle for the combination. You get the idle speed down by doing idle timing first, not the other way around.
There can be a host of reasons why the idle speed is 900 rpm & idle vac 14-15". Cam installed in a retarded position &/or low comp ratio are two that come to mind.
The OP sounds like he wants to tune the engine as best he can without pulling it apart....