New 408 stroker runs rough at idle

I set the ignition timing at 10 degrees btdc at idle, and with the engine warmed up at 700 rpm,
What is total timing at, and why trying to idle at 700 vs 800, even 850.

10 initial is low, but need to know what it has total first and foremost. That distributor may only have 10-15 degrees of sweep, pending what has been done to it. Hard telling if you don't verify total .