Just for information, the 10.25 is a factory number and is higher than reality. The early 340's were actually approximately 9.4-9.5 static compression ratio. It seems like all the of the Mopar factory compression ratio numbers were about .75 points high; I suspect they were based on combustion chambers that were milled to something like NHRA minimums. (And perhaps NHRA minimums were based upon some theoretical factory minimum chamber size that the factory used for marketing purposes.)
