If you hadnt replaced them already I would vote for radiator been cloged..

anyway
first of all DONT let it overheat. the head is prone to crack.
second. your headgasket is been "eaten" slowly by the overheats and propably it will be burned in cilinder 4 the one on the firewall side - personal experience <img src="/forums/images/graemlins/smile.gif" alt="" />

so whatever you do dont let it overheat again.
to be on the safeside i would comlpetly remove the thermostat. The increased flow will keep things cool until you find what it is.

2 gueses ( if the new radiator isnt cloged by some kind of "debries" lets say)
radiator fan
and water pump
in this order.

throw the stupid fan mecanism away and do your car a favor and put an elektric one.

After remouving the thermo take the radiator cap of and with a cold engine start it and look if you see any strong flow of water

a less possible but cheap nevertheles is that the radiator cup is stuk and doesnt let the expanded water to flow to the expansion bottle ( and/or remove posible air by sycking water from the botle to fill it properly.

an other wild guess is that the so called cooling device on the base of your oil filter does not work right.
Dont forget oil also cools engine, spesialy in ours that has an oil jet underneeth the pistons spraying oil on them to cool them