I got this info from "The catalog of Chevelle, Malibu & El Camino ID Numbers 1964-87" :
6BHC289-1
6BH is a 2.29 (posi from 1978-84 and non-posi from 1985-87)
C assembly plant is Buffalo
289 day of year
1 shift { 1st (?) (my book only indicated D & N for day & night)}
Doug