I saw these numbers on the back of a small block with the bellhousing removed. They were above the crank:
678636 386371 H35
The H35 is not a casting date. The casting date was in the normal location.
'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles