Hi. The optimal 427 SO Blocks were produced between 1966 and 1967. The 1968 Blocks were the last of the line produced to be installed in production vehicles. These Blocks differ from the earlier SO versions in that they use Hydraulic Lifters(and thus, had Hydraulic lifter galleries incorporated into the design). The earlier SO Blocks were for use with Solid lifters, and had no lifter
oil galleries. Arguably, the 66-67 Blocks were more 'race' oriented than the 68 Blocks, and probably of a higher quality overall, but I know lots of cars that run very well with 68 Blocks in them and live.
Core shift occurs in casting when the cores(inside the sand boxes or molds) either move, are off center or off axis, are not level or partially collapse as liquid is poured into the molds. This basically leaves parts of the mold filled to capacity and parts that are lacking material(either at the top, bottom, sides or a combination thereof). Core shift leaves one(or more) parts or areas of a cylinder wall(or outside wall, or deck, or main bulkhead, water jacket etc) thicker at one(or more) points than at others, and, if it is severe, may limit the engines ability to be rebuilt, overbored or even initially assembled. As companies went to thinner casting techniques, core shifting became more of a problem on more Blocks, especially those destined for production line car installation like the 68 Hydraulic lifter 427(produced in large quantities), instead of Blocks specifically produced for factory 'race'(NASCAR, Drag, Road Race) applications(produced in smaller, more controlled quantities).
To answer your question about value, if I had an NOS 67 Block(I do) and an NOS 68 Block, I would price the 67 Block at at least $1500.00 more because I feel it is a stronger casting. Keep in mind that most Cobras that were equipped with 427 engines would have had a pre 1968 Block in them. None, to my knowledge(which may not be as extensive on the subject as other members), was produced with a 1968 Hydraulic lifter Engine.
Also, keep in mind that the SO Block was designed for an engine that was NEVER installed in any Cobra in the first place. It was designed for the 427 SOHC, and adapted to the wedge motor after the ruling by NASCAR against allowing the engine to run in competition.
When looking at your 'patch' remember that Ford sometimes patched blocks at the factory depending on how hard pressed the schedule was to produce engines, parts and Cars. A factory repair will usually have a smooth surface and have 'bubbles' in it. If yours looks like this, it was 'professionaly' done by the factory and will outlast the rest of the Block, lol.
In any case, there is some info to mull over. I looked at the pictures with a 10X glass and feel as though you have a very nice car to drive and enjoy for a long time to come. Hope this helps. Dennis, DSC
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