Junkyard 5.9L Magnum + Edelbrock LA heads build

It is a matter of the relative temps at the start of combustion, the temps during combustion and the temps at the end of the power stroke. So if the absolute temps vary up or down, but the start, middle and end temps stay relatively the same, the pressures, torque and etc. will be the same.

FWIW: With your dimensional numbers, I am getting 8.9 SCR and 7.2 DCR at sea level (which is the difference I would expect with a cam with advertised intake duration of 274), with 6.2 effective DCR at 5000'. So, yes on the rear gears.....