The 223 Remington cartridge was introduced in 1964, so I think they probably did not produce the 760 in 223 from 1960-1964. Even if they had, that was over 50 years ago, and the durability track record of the 760 wasn't the best.
The 7615 version of the 760, more like a pump action AR, and even so they did not offer it for very long 10+ years ago.