I was curious (and a little bored on a Monday morning) and found this. I am a researcher, after all.
(DISCLAIMER: I HAVE NEVER, NOR WILL I PROBABLY EVER, RAN A RELOADER. I'VE NEVER EVEN SEEN ONE IN PERSON.)
Look at the hull knock out tool, and see if it a solid rod, or a spring loaded cup.
The old non C will have a solid post knock out rod, while a newer C tool set will have a spring loaded cup knock out tool instead. In the below photos, look at the tool by the handle. the machines are the same in both a C or older non C, and its the tool set that is different in the machine instead (so yes, an older not C can be upgraded to a C machine.
This is a 375C,
![Image](http://www.gamaliel.com/images/PW375duo_matic_L.jpg)
This is a non taper crimping 375,
![Image](http://i121.photobucket.com/albums/o223/HEAD0001/IMG_0355.jpg)
And to throw you a curve ball, here is a 16 gauge 375 tool set, with a 12 gauge 375C tool set in the same head (not installed in the head is the pre-crimpers for both).
![Image](http://picturearchive.gunauction.com/8584105237/11154314/SUC51020.JPG)
Staring from the front center tool and working to the left cockwise,
12 gauge deprimer, 12 gauge C knock out tool, 12 gauge c crimper, primer tool, then drop tube.
On the center back and working clockwise,
16 gauge deprimer, 16 gauge knock out rod (375), 375 crimper, priming tool, and drop tube.
So yes, you can have the machine with two different type tools sets up in the head, since to change gauge on the machine, you pull the head, rotate it 180, then change out the wad guide and sizer for the tool set that you will be using.