Sam, I believe K-Line was pretty consistent in using a single R2LC and single motor driver, either a non cruise Lionel DCDR or their own K-Line Cruise board to drive 4 motors.
It seems to work but I think its safer to use a separate motor driver in each powered engine. I was able to use a single radio board to drive a pair of ERR Cruise Ms in a pair of E8s. Worked great and there is no sign they are fighting each other. It required a new tether though and multiple connectors so took many more hours than using two identical radio and motor driver boards.
Pete