Setting vacuum advance

A little follow-up. I measured the vacuum and have about 5" at warm idle in 1st gear at about 950 rpm. That's with timing (all mechanical) at about 13 deg.
2000-2200 rpm going down the road in 3rd gear is about 12" vacuum. Don't recall the spark mech advance number. (Cam is 251/256 @ .050)
The carb has an unknown power valve (no markings!!) so I have no idea if it is open at idle or not. I do know the engine is still rich at idle so going to try a 3" power valve just to see if it improves the rich idle condition. That may not work for driveability but we'll see. It will be awhile before I get to work on the dist to limit the max vac advance.