Ya know, any radio will work. From the cheapest AM radio to the highest priced FM radio. That's the good thing about the M18, it doesn't need all the fancy bells and whistles like racing Touring cars or trucks.
I have the Novak SPY in my M18 with a small Futaba receiver and Hitek MG81 servo and it's perfect. The HS55 servo is too small for the M18 and would break easily since it's plastic gears and there is no servo saver. I would suggest the 81 or 85MG servo by hitec.
Hope this helps.