Supercuda & Mike P ...thanks for straightening me out on the issue. For some reason, I assumed that the Chrysler Hemi/Poly had the same factory compression rating as the Dodge.

Mike - thanks for taking the time to document all this work. The 270 is not the last engine in this series that I will be building.

This discussion raises a question... probably could end up hijacking this otherwise useful thread... what do we call these engines? The group that includes:
DeSoto Hemi
Dodge Hemi
Dodge Poly
Chrysler Hemi
Chrysler Poly
...wasn't there a Plymouth version...

Is there a single name used to describe engines of this era? I guess not because I realize that few meaningful parts were shared among most of them.

Anyway, back to your build. Thanks for sharing.