I have a Chicken swap question

The halves will be fine. Make the recipe as published.

The chicken in the Ina Garten recipe is "spatchcocked." This is easy to do. A butcher can certainly do it, but all it involves is snipping out the backbone with poultry or heavy kitchen shears and flattening the bird by pushing down hard with the heel of one hand placed over your other hand. You'll hear the breastbone break. I remove the keel 'bone' first, but you don't have to. Look up a YouTube video on spatchcocked chicken. No need for me to explain in words what's easier to see.