Cam shaft duration plays a large part in initial timing, quench and combustion chamber design plays a large part on total timing as does fuel octane,engine temperature, fuel ratio and engine load.
Having said that my 422 liked 18 initial 34 total all in by 1800 rpm, oh and 52 with vacuum advance maxed and engine temp at 165. 3.23 gears and overdrive. I pulled 21 MPG on several 300 plus mile trips.