Have any of you ever seen a 66 square port 858 head without the bosses and small threaded holes between each exhaust port for mounting spark plug shields?
On my new acquisition - survivor 66 L78 - the Passenger side 858 head has the bosses and holes as it should. And every 858 head I have ever seen has the bosses and holes, and Colvin's Chev By the Numbers book also says that they all have them.
67 square port 391 heads do not have the bosses.
While I was inspecting the car, I saw no bosses or holes on the driver side head, so I was afraid that head had been changed, or thought that maybe it was an extremely early 391 head since this is a July built car with a T0630EG engine. So I removed the valve cover, and it is in fact a 1966 858 cast head, with date F 17 6. Perfect for the assembly date of the engine.
I have pics of a set of F 22 6 dated 858 heads that do have the bosses and holes. So obviously Tonawanda did not change all the 858 head molds at same time. So I can only speculate that they must have changed one mold as a prototype, cast some heads, they worked okay, so they just used them in regular production and one ended up on this car.
See the pics. First pic is the driver side weird head, no bosses. Second pic is the casting number of this head, and third pics if the casting date of this head. I did not remove the valve cover on the passenger side yet to check the date on that side.
Any other ideas?
Thanks - Jeff
