Low compression 340 VS high compression...

Ok, so dig this.

https://www.summitracing.com/parts/...J7eR3gK7oPfKCTkhJw3qWS4aj6Kro3r9GbFWd6Nfu27_T
That's the standard version of the piston I posted above. Notice here they have it at a measured POSITIVE 10cc. The fuckers. That's probably correct. I don't know where your 13 extra ccs is comin from, but 10ccs is about right for that piston top. I also ran the numbers for deck clearance using the UEM deck clearance calculator and got .002". well within tolerance for Chrysler's stupid deck machining practices.