Marshall, who was with Caughey for two of those world title wins as well as five of his nine national championships, has finally got the all-clear to begin the rebuild of her Christchurch home, which was damaged in the Canterbury earthquakes.
Caughey has tapped Canterbury's Shama Putaranui to join him, having previously navigated for Australia's Group A national champion Brooke Dixon.
"It's not easy finding a good navigator with the right attitude and the ability to think and respond quickly while operating in what can be a fearful environment," said Caughey on his website.
"And also important to our light-weight SuperBoat Sprintec package is Shama's petite frame - like Karen, she'd struggle to tip the scales at 50kg, and given they are of similar build, she should be able to step into Karen's seat for this vital two weeks."
Dixon has also arrived in Missouri and will be stiff competition for Wanganui's hope in Richard Murray in the Group A class.
Murray finished fifth in the national series and had to race against time to get his Ford-powered Mean Machine back up to scratch after a heavy smash in the final round down in Wanaka in April.
After the boats were sent on their way back in mid-June, Murray's wife Julia said they flew out last Saturday and had a few days in Las Vegas before heading to Poplar Bluff.
"We are then heading to New York [Niagara Falls], Atlanta, Tennessee for a Nascar race with 140,000 people attending, and then fly over to Lebanon, Oregon, for the final round on August 30-31."
This year's national Group A champion Sam Newdick of Hamilton is not attending the world series, but third-placed Paul Gaston is there as part of the big Australian contingent.
The other Wanganui contender in the Superboats is Rob Coley behind the wheel of Poison Ivy and, like Caughey, he also has a new navigator, but one who is certainly used to the fast lane.
Wanganui drift racer Ricky Lee has joined with Coley for the Superboat series, although he will find there is a big difference between burnouts in drift cars and the g-forces which come from a 705 cubic inch methanol engine boat.
Coley had been supervising the journey of the North Island-based competitors boats, which sailed by ship for 35 days to Portland, Oregon, then travelled 4800km by truck to Missouri.
After this weekend the boats will be driven back to Oregon for the second round of the world series at the Global Jetsprint Track at the end of August.