all the pictures that i can find make it look like a 1600. The grill  on my machine matches the 1600 but the grills I find on 770 's are compleatly different. They might be earlier models. The only posting of numbers I could find did seem close for both 770's and 1600's . Are they significantly different in mechanical setups? Again the #'s  that I found on the dash are 47-704 and 149-045 725. I will try to give you a call sunday afternoon. Thanks again. 
Daniel