3956618 block used on 68-69 A,F and Corvette 4 bolt, 69 302 Z28 4 bolt, 69 327 Fullsize car 2 bolt and 69 350 cars 2 and 4 bolt.
C259 block cast on march 25 1969
V0327HN Engine build date at Flint on March 27, 1969, HN could be either 327 full size or 69 350/300 hp 4 bolt full size.
I noticed also the the HN suffix code was used in 65 for the Corvette. (Nastyz28.com)
Dave