Thee are several differences between the two. Look for words like "new style" or "later style" in the parts description of the new model schematic.
Rigger - do you have the old FCG? The firing pins might be the easiest to access and compare to the drawings.
Also, if it is a 17-shot capacity or a Glenfield model I think both of those are "old" style, but I could easily be mistaken. I know that my 14-round model is a "new style".