273 Build

MOPAROFFICIAL said
Measured one chamber on the 302's and the 920 heads that have a valve job, hard seats, stock valves and of course the typical .003-.005 milled off.
65.5
Safe to say they were around 66 or so cc's from the factory.
The 302's are still 64cc.

It looks like it's best to use the larger chamber numbers of those posted. I don't know where they came up with those 57cc chambers!