You can go to Numrich gun parts and compare certain parts of
your rifle to the schematic on this page:
http://www.e-gunparts.com/productschem.asp?chrMasterModel=082Zz80
I have a Model 80 old style (made somewhere around 1935 I
believe. The easiest way to tell if you have an old or new style is
by looking at the bolt. I can describe the new style as having a
larger bolt handle and the handle is set back from the breech face
a bit farther than old style. The old style bolt handle is also
swept back just a bit.