HELP! 66 cuda idles fine, but not when in gear

Also with that cam, 16* at idle would be minimum, maybe in 408. IMO 18* -20* will be closer to ideal depending on the heads, compression, etc.
Distributor starting point for a curve

That's 18* from 0 to maybe 900 rpm. Should be able to get it to idle around 900 rpm give or take some when its warmed up and choke is off.