I suppose the water for the heater was taken from the thermostat housing so the motor could warm up quicker, rather than trying to heat the heater core as well. Probably makes no difference though really. You need a tap otherwise your heater core will always be hot and its going to heat your cab up as a result, summer and winter.
No idea on electric heater, might be available.
No doubt someone could fit extra outlets on your radiator (for heater hoses) somewhere and you could hide the heater hoses more easily then.