How much does every .010 decrease chamber size on the closed chamber heads? Trying to get BGE head to eagle chamber size.

Here is a good compression calculator.... https://diamondracing.net/p-10-compression-calculator.html

He is not looking for a calculator, but the information for how many thousandths need to be removed to reduce chamber volume by 1cc

.0065" off for a 1cc chamber reduction was the figure i found for closed chambers . In reality my Apaches required .020 off for a 2.1 cc reduction , But ! that was after some chamber work and a valve job.

Thanks, thats what I needed to know. So double check my math, I need to remove about .030 to keep them roughly the same size?

Early 5.7 85 CC
Eagle 5.7 67 CC
SRT 6.1 73 CC
6.2 and 6.4 73 CC

Is it OK to take off .030 on my BGE heads?

Assuming your basing it on .0065 for 1cc , then my math says .030" of would be a 4.615cc reduction . i think an experienced machinist will get what you want .
Remember to deepen the rocker shaft oil feed slot by the same amount removed from head.