best to do everything at the same time, though its not a must. that way everything is on the same maint schedual. but you are talking just cap and rotor, not whole distributor, right?
the idea is that you replaced wires and you have old plugs, cap and rotor. but if the old cap and rotor isnt in as good of condition, your loosing a small amount of energy. but i think w/all these hei systems your fine.