Dating ss 69
This allowed for larger plates and thus more cranking power.
67, 68, and early (pre-May) 69 L6, 302 (Z28), and 307: The standard battery was the Delco Y55.
The R79 battery had two different size terminals, a 3/8-16 positive terminal and a 5/16-18 negative terminal, so the terminals could not be interchanged.
(The R89 battery replaced the R79 in 1971 and had the same basic exterior dimensions, but the R89 had a single terminal size, 3/8-16.) 67-69 RPO T60, Heavy Duty Battery: The optional battery was Delco R69, a 70-Ahr battery with top posts and standard terminal positions (positive terminal inboard).
In contrast, the opposite end of the SS spring is oriented at about -75 degrees - or a full 180 degrees from that of the non-SS spring.
The Y77 used standard terminal positions, not the reversed polarity terminals like the Y55 it replaced.