So after getting home and seeing the pictures on my computer (yay, bigger screen) and going on Google, it appears that the girth that comes with the Tough 1 harness is a wrap strap style, and you'll have to use the nylon straps at the bottom to wrap around your shafts. Urk. Maybe Taffy can chime in here since she has more experience than me, but I'm not sure how well those particular tugs with the wrap girth will work when your shafts are already pretty low.
Too bad you didn't have shafts like these
It's too bad you couldn't return it. You look like you're going to need longer traces to set the cart shafts back further, and will need to find trace extenders (guess that's kind of a trade off with the sewn in traces vs the buckle in ones, but then, I've always had buckle ins)
Just curious, but is the tug strap just sewn onto the saddle?
It's water under the bridge now, but it's too bad you hadn't gotten this harness instead ( Amber Hillside Horse Harness - Formerly Rons Horse Harness - Liberty Harness ) I couldn't afford the Comfy Fit when I needed to start looking at harnesses, and almost got the Tough 1, but decided to look around first and found a good review on that one, and decided to take a chance. Their comparison photos sold me, and when I received it, I was pretty blown away with how nicely it was made. Ah well.