X-heads vs J-heads: what's the difference??

As Advertised by Chrysler

1968 thru 1970 ~ 340..... 10.5 - 1 Compression-Ratio
1971 ~ 340..................... 10.3 - 1 Compression-Ratio

Piston Height the same for all 4-Years.... +.045" AB {Above Block Deck}
Head Gaskets the same for all 4-Years.... .028" Thickness

Note; According to Chrysler, the later {mid-1970 and later #2531894 'X-Head'} Cylinder Head Castings
had approximately +2.0 CC's larger Combustion Chambers than the earlier Castings.