No never actually been on any portion of the 6 foot Track, except the end at Jenolan Caves.
With St John Ambulance, I use to provide First Aid at the Jenolan Caves Finish Line for the 6 Foot Track Marathon for a couple of years, but never been down to the Coxs River or or the Bowtells Swing Bridge.
The closest I had been to Bowtells Swing Bridge, was exploring a couple of the State Forestry Areas on the West side of the Coxs River, but never made it down to the Coxs River itself. I don't really like National Parks that much, and as I'm not built for walking, and the fact NP's lock out 4WD'ers so much, I try to avoid NP's as much as I can, would prefer to give my money to NSW State Forest, at least they only lock you out for your safety when logging is going on.