I have tried the magnet approach. I found that neither set of fins seemed to be metal, or at least not a magnetic metal. I thought I had read somewhere that the metal fins are an alloy or such like and therefore the magnet approach isn't going to work.
i bought mine as steel internals and they are NOT magnetic on either side, the 360 bearing has TT stamped in it so i presume rebuilt by turbo technics, heres a pic of exhaust side (not very good pic) so does this mean i got bumped by the seller ? http://i43.photobucket.com/albums/e362/daz2206/turbo4.jpg
To the best of my knowledge they are actually some form of iconel alloy, so the magnet doesnt work.
It looks like the nut found on the standard shaft of the ceramic turbines, I dont know why it would have been reused so my guess would be they are ceramic (but then again, theres a 50% chance they could be 'steel').
Get them checked out by a turbo specialist, its the only way you will be 100% sure. One thing I can tell you is the previous owner liked running octane booster