dont now the 350 motor.. but in the 600 RFVC motors, the only difference with the cranks XR\XL it's the balancer gear: the XL has "elastic" gear system (smoother @low revs), the XR has normal "rigid" gears coupling.. so you can mount the XR crank in the XL cases, but must match it with the XR's balancer probably the 350s have a similar setup