I have to say all of what I have read here seems a very bad idea.
I see no problem with using either rad, on the ST the 1.2 style rad still has an expansion bottle.
What ever you do, dont play around with the rad cap or the vent pipe. Quite often the system will chuck out a bit of water and then be happy where it is.
FYI the expansion tank will fill when the engine becomes hot, once it cools down it will suck most of the water back in.
Dont use the expansion tank level as an indication of the system level. If you fill the system when cold right to the top, then leave the expansion tank exactly how it was the systme will chuck out what it doesnt want when its hot on the next run. dont expect either of the radiators expansion or not to always be full to the top.
