well, it doesn't need a compression stroke, so you might want a cam with twice as many lobes and no overlap.
Also you need to plumb hot high pressure high volume steam to the intake ports, the same sorts of heat and pressure are needed as during regular combustion to make a similar amount of power.
Need some sort of throttle to control the steam being sent to the motor.
it might need more lube, maybe the oil control rings can be augmented, dunno.
I'm sure it's been done though,