Hi Buckstix, unfortunately my memory faded the details a bit. The Jack O'Connor article on his safaris' including those when accompanied by Fred Huntington, does have a photo of Fred posing with a Zambia lion but the rifle in the photo was his 300 Win Mag that he had as his light rifle. There is a photo of Jack posing with his 416 and a downed buffalo and mentions that he used his 416 in Zambia in 1969 on the best lion he had ever taken.
Jack does enumerate that both he and Fred turned the belts off 378 Weatherby cases to load for their 416's and used bullets obtained from the Colorado Bullet Company and steel jacketed ones from England.
The photos in the article are quite small and do not provide a quality scan.