I have only seen them used for racing Standarbreds. I am picturing the harness shown on the Standardbred on the Walsh site.
http://www.walshharness.com/walsh
Sorry, this is not going to be a good driving harness for your needs in non-racing driving. Quick hitch harness is specially designed for specific use in racing with a race bike, on a groomed track. Actually a “total system” of attaching horse to specific vehicle, so things all work together.
You won’t find those conditions or use that vehicle, out pleasure driving.
The money needed to change things around to “sorta works” for pleasure driving, would be much better spent in getting a pleasure driving harness of the right design.
You are NOT doing your horse any favor, by changing things to fit the racing harness design over into pleasure driving. Horse will probably get sored up fast, pressure of pulling is not well placed with this harness. Horse trying to pull even the light weight of a Sprint cart whose balance has been radically changed with different shafts, driving over various terrain of fields, show ring, down the road, is going to cause various problems. You go out pleasure driving for a while, horse will use most of his body. Race conditioning is to EXTREMELY light vehicle, no surface changes on the groomed track or paved roadways going to the track from the barn. Body use is limited in flexing, gait changes, use of the head to move his load.
Harness may be a great buy, but not suitable by it’s design, for pleasure driving and the vehicles used for that activity. Kind of like taking a Western Saddle and trying to do Show Jumping in it. Great saddle, just not the saddle for that job.