Thomas,
Full background on the C8ZE head is this. In mid '67 when the '68 line up were being organized for actual production, the "initial" plan was to release a "HiPo" 289 but that quicky changed to a HiPo 302. Several "revised" parts were "pre made" so that engine assemblies would be in place when car production began. The HiPo 302 package was to include the heads you are looking at , the C8ZE version of the 289 HiPo balancer, the C8OE 302"HD" rods with 3/8ths rod bolts ( Later sold off as Muscle Parts) and some other parts as well. That engine was dropped at the last minute in favor of the more exotic Tunnel Port 302 which was eventually dropped too. None of the "higher performance" ( beyond the "J" code) engines were made except as "prototype" engines never installed in a production car. This resulted in a large inventory of pre made parts for non existent engines. So those parts were "sold off" through the Parts and Service Division as "replacement parts"
In other words , none of them were "created" to be sold over the counter as some have suggested. Except for smog passage revisions , the C8ZE head has the same potential as the earlier C5OE versions. They are usually valued less because they are known as "over the counter only " parts as already mentioned.
Randy