Hey I've worked with a steadicam op as an AC for a while and we always used a Small HD 702 and Paralinx Arrow+ SDI
I had fantastic results with 600ft of working distance!
I used his Cmotion Handset and Camin 4m Reciever with 2x M26VE Heden Motors for follow focus.
You can also rent Preston FIX Kit or Arri WCU-4
Don't forget to make sure to have a Cart with a docking stand if the steadicam op doesn't have one. Otherwise someone is gonna have to lug around a large Matthews stand everywhere you go!