Leo Santucci in his book says not more than .030 of the block deck of the 292. That may not be the definitive answer and we will have to wait for Twisted6 to chime in.
3cc out of te combustion chamber shouldn't be a problem. You have the Integral head most of us are not familar with the Integeral head. You might wnat to go to Twisted6 web site. Look at the heads he has pictures of there, they are the non-integral heads. If the combustion chamber is pretty similar, then unshrouding the intake valves would help and at least 3cc.
Larry
