Roy,
There are two "original versions" of the C6FE iron ,289 , GT40 head. Type one is as you mentioned with cast in spring pockets like a HiPo. Type two does not have the cast in pockets. This isn't a simple machining thing , it was a revision to the casting. Neither used guide plates as the guide was in the pushrod passage. "Originally" the 1.875 dia intake valves used a 30* seat angle and the 1.625 exhaust valve used the more common 45* angle. The casting number is on the outside ( all) as well as the inside ( on many , but not "all"). They all use a conventional 289 HiPo stud and rocker arm assembly. The combustion chamber is also revised and is larger in volume than a HiPo head. The ones from SAI had the "banana water ports" welded up. Ford and Bud Moore didn't do this modification. The heads are prone to external cracking just above the lower bolt holes. It is common to see them repaired and the repair if done right is bulletproof.
The heads were reproduced in the 90's and "289" was added in the valley area. If it is there or you can see that it "was" there , you have a repop head. Those head casting cores are now owned by Cobra Automotive and have had all the "issues" corrected. "New" ones are virtually the same cost as used ones but are FAR superior. I have owned 7 sets of originals in the past . They ranged from NOS to those ported by Valley Head Service and Mondello. I am looking forward to a new set from Cobra Automotive.
Randy.