73 360 Ignition timing after Chain replacement

Gloyale said
Vacuum is steady at idle at 21 inches.

Gloyale said
Mixture screws are 1-1/4 turns out.

Gloyale said
I live at 400.

This says it all.
Yur cam-timing is fine;forget about it
21 inches points to the 15* of Idle Timing; but if you don't have detonation at WOT, then just drive it.