Greg,
What you figured out makes sense. However, the mounting pad holes are for the larger G size box (don’t know the number). So that leaves one to either use the larger box and the #1 coupler, or drill new mounting holes.
The reason I posted this, was because on my snow dozer the couplers are mounted at 34.5" centerline. This is quite a bit higher than the Kadee recommendation, so I don’t think they would play well.