Well, those headers appear to be the Hooker Super Comps for A bodies with the one drivers side pipe under the K frame.
As far as a stock head making the HP, the MP 380/360 create engine consistently made over 400HP with dead stock heads.
The MP cam was IIRC, 230@.050 intake.
Idle quality with that cam on a 112 will be smooth. Not so much a "Muscle car" cam idle.