Here I show a comparison of the numeral. I am guessing that there are at least six unique types, and perhaps more. It is easy to categorize a single type as two because the same type can look quite deferently depending on wear.

I found one type repeated and with a small bump at 7 o'clock.

I also find a few other with breaks. These look like breaks and not gaps caused by the angle at which the mark was punched on the stamp.



I also have Picasa web albums of the stamps and the numerals here:
http://www.somestamps.com/pages-articles/351-400/article351-200901-cuatro-cuartos-1860-RC-2-picasa.html