1680 has a larger rotor also, larger concaves and grates. Sieves are larger, is it a short or long cleaning system some 80's came with a longer cleaning system with the old style fan. 1680 also has more power.
Agree on above, also sieves wider, more HP, main front axle wider stance, rotor diameter 6" larger, separator clutch disc type as 60_66 is belt clutch, rear axle spindles bigger.
