Warner Bros. shut down all production in April and May of 1953 to work on developing their new All-Media camera rig. All films shot prior to that time had been photographed for 1.37:1. However, quite a few were in the can in the Summer of 1953 and that's why you see 1.66:1 and 1.75:1 being recommended in that Exhibitor listing. The studio looked at every film in each ratio to determine the one that worked best although the titles and compositions were certainly compromised in widescreen. (Columbia was the only studio to modify opening credits to favor their 1.85:1 house ratio.)
On May 7, WB officially announced the studio was 100% widescreen and would be composing all future productions for either 1.75 or 1.85. The new All-Media camera rig was first shown to exhibitors on May 19:
The studio resumed production on location in Camargo, Mexico for HONDO on June 11. The first new film to shoot on the Burbank lot on July 16 with the new rig was THE BOUNTY HUNTER in 3-D, Warner color and 1.75:1.