Yes digitals will work on AM/anologue radio sets but it wont work to its fullest potential. Its best to be used with high end radios that are fully digital most radios have a function to have the radio transmitter set it from digital to normal frame rate. if you want a good servo get a FET servo. And what you look for is torque and speed. for steering 8kg+ and .1 secs or faster. and for throttle, .1 secs or faster torque is not an issue for throttle. for electric cars 4kg of torque will do but the speed principle applies as the same for gas cars.
Hope this helps.