No worries, no matter how I approach this, my Husband is always looking out for me. When I showed him pictures of my instructor took at the Skunk River competion, his reply was, "you can get carts with 4 wheels? Why didn't you, that's much safer"
When we drove single, our cart was the same. You slide the trace over it, and put a pin in it. We've driven like that without incident, even with a possessed old mare trotting mach five down dirt lanes. We did not use a lynch pin, but I couldn't tell you the official name of the pin we used. We only have one mare that we use our breast-collar harness on, and that is how we hooked her to the cart. The rest of our harnesses are collar harnesses and have chains on the end of the traces. Here is a photo of said mare, I believe this was the last time we drove her so far this year. She's 23, and mostly a pasture puff these days. This picture is quite old, so excuse that her harness is a bit sloppy. Seeing it in the picture really makes me want to go and fix it!
If you look in my albums under stanley your answer lies there.
I have a set that could go through your swingle tree holes so the end bolt would go through and the quick release through the crew hole on the traces.
Or have a pair of traces made up with a steel ring at one end so as to make hitching up realy easy.
Ill have to supply you with quincys pictures.