5.2/5.9 H.P build guesstimate

Hey! Yeah I’m going with the 360 Magnum engine which has true 9:1 compression the car will have 3000 stall converter and 3.91 gear set at the drags and 3.55 on the street
I love magnum 5.9's but are the magnums a legit 9:1? Every one I've pulled apart has a dished piston about .040 down below deck height?