Correct,
The Factory 'advertised' Compression-Ratio is way off the charts when compared
to 'actual' measurements.
Back-in-the-Day,
That is why Mopar recommended milling the Cylinder Heads {#2843906} for the
1968 and 1969 '383' {.030"}.
It really got you back to around {10.0 to 1} Compression Ratio, without touching
{decking} the Cylinder Block.
And you were fine, with Valve-to-Piston clearance, with the recommended Street Performance {484/284} 'Hydraulic' Camshaft.
