It’s the unposted ECZ-G heads that appear to have the most issues with blowing head gaskets either when the compression ratio is stepped up or the heads themselves have been milled more than 0.025”. The ECZ-C heads are cast differently in the water jackets around the intake ports and because of this they do not have the same propensity for blowing head gaskets on cylinders 1, 3, 6, & 8 like the ‘G’ heads do. Here are a couple of links to past threads on do it yourself posting of the G heads.

http://forums.y-blocksforever.com/Topic33877-3-1.aspx#bm33879

While detonation is a key player in the head gasket failure in un-posted heads, the actual head deck thickness is still the major consideration.  The un-posted G heads simply have thin deck surfaces as delivered from the factory and as a result there is a balance point between the compression ratio and amount of head mill before gasket failures will be prevalent.   A less amount of head mill and more compression or more head mill and less compression is the balancing act that must be played with the un-posted G heads.  But ultimately there is a point of no return where excessively milled heads simply do not have enough internal support in which to hold the head gasket firm regardless of the compression ratio.  So with that taking place, retarding the camshaft would not help.  The Ford manual is pretty specific in limiting milling of the ’57 heads to a maximum of 0.010”.  Once the heads became posted, the rules changed and more aggressive milling or increases in compression ratio could take place with less chance of head gasket failures.

Un-posted G heads can have posts added to cylinders 1, 3, 6, & 8 which will give these particular heads another shot at being used successfully with higher combustion pressures or save a set of heads that have already been milled.

Try this link for how to spot posted heads.