340 Pistons with 10.5 CR with X Heads???

So running some numbers on Dynamic Comp ratio with a cam that I might use. The Comp Cams XS274S 236/242 @.050 536/546 with 1.6-1 Rockers, Intake closes at 63* ABDC. Specs here.

Keith Black 243's
Assuming that after my valve job my chambers are 70 cc's
using a .040 Gasket
@ about 700ft above sea level

Static 9.74
Dynamic 7.70-1

So I still think I would need to do some milling to get the compression that I want.