You are correct in assembly plant and date. CTY was used for the 375 horsepower 396 (actual displacement is 402) in the Chevelle and Camaro. It was coupled to a TH 400 transmission. Also designated on the build sheet as “SHP” i.e., special high performance.

In 1970, 2,144 Chevelles were made with the L78 396-375 horsepower engine and 18 were additionally optioned with the L89 aluminum heads. Only 600 Camaros received the L78 – none with aluminum heads. If you have aluminum heads (that are original GM), you most certainly have a Chevelle engine.

I don’t know of any source that breaks down 4 speed versus TH400 automatic transmissions for Chevelle/Camaro L78.

Where exactly is the 10A10? The reason I ask is that Tonawanda warranty engines were sequenced from 50000 to 79999 but when that quantity was reached the sequencing began again with 50000 but the letter "A" was added to note the rollover.

Regards,
Glenn