Tom,
Actually, that "number" belongs to a 69 Pontiac, but because rebuilders commonly change housings, it's found its way to your 69 SS 350. Remember, they could care less about date codes and casting/stamped numbers, so you'll find starters on Chevrolet cars with housings from Caddys, Buicks, Olds, Pontiacs, Trucks, etc... They all fit!
Ed