66 SS Chevelle block casting date vs assembly date

[MYSTERYCHEVELLE]

Okay.. Here's a question that has been asked many times, but I guess until it directly applies to you, we don't pay attention as much as we should so humor me....

I recently inspected an extremely nice 66 SS L-78 that was framed off, done to the highest level ( used the 66/67 SS FACT BOOK ) and is just plain spectacular. It has a POP and previous owner titles and very detailed owner history, has great before, as found photos, and complete restoration photo album. The POP is Real in my so called expert opinion and the DECK stamp is original in my opinion, Trans is non orig. and this was stated up front at time of purchase and Rear is original.. Heads, idler pulley, carb, etc.. TRIM TAG and VIN TAG are unaltered... Nothing about this car raises an eyebrow to me in the form of fraud, restamp, or fake docs, etc.. and the resto is top notch and I am hard to please in this regard, esp. with 66 SS's.

but.. yes, there is always a BUT!!

The assemby date of the car is May ’66. but the block casting is K5….it is a a 962 Block as it is supposed to be too.

I’m stumped.. I know the drill when it comes to what is the considered acceptable month span for this type stuff.. but I am having a real hard time believing this car is not the real deal.. if someone goes to the trouble of trying to pass off a car as real numbers matching, and supply you with a multitude of docs, pictures, owner hx and names.. and even if they Re-stamped the deck so well that most would be fooled..( including me ) would they not have found and used a closer casting date block to do so??? Makes no sense?? Not saying someone trying to deceive has to be very smart. But I still find this hard to swallow… they get it all right, to the point of no raised eyebrows.. but they don’t use a block that is closer in date to the car??

So, my question to you all.. anyone else have a similar situation? Known numbers car with casting date and assembly date that doesn’t jive? Or anyone have any insight.. ie.. the stories of blocks that were pulled off for a possible problem and then installed later…

The L-78 engine option was cancelled on May 11 1965 and was not available in the beginning of the 66 Chevelle production year ( July/August 1965 ) but was then reinstated on Oct. 7, 1965 and the dealers were given inserts to show the engine option now available. This is a Kansas built car if it matters, which I don’t believe it does.

Comments welcome

Thanks

Mike Crown