My opinion is that you have already addressed compression sufficiently(by zero decking)and should concentrate on flow for additional improvement. Installing larger powerglide intake valves (1.94" dia. GM #3835519) will improve inbound flow and for exhaust open a valve halfway and measure the distance from the valve head to the combustion chamber wall. While doing this you should notice a lump on the chamber wall in that corner and by altering it to unshroud the valve exhaust flow will go up. To see pictures of an 848 head cut thru several planes and observe wall thickness click on webshots in my signature and then the 848 head album.
