9770sts head

I bought a 9770 combine last winter and am now looking for a header. Primarily looking at macdon fd70/75. I am wondering if it matters what series of deere it came off? Many of the fd 75s came off of a S series and I am just wondering if there are any changes made there that could cause an issue. Especially if I buy something at an auction. Also unsure if the 9770 can handle the weight of a 40' head, or does it need a certain size of cylinders or a third one? Previous owner had a 635 flex on it. It does have contour master if that mean anything as far as how it is set up. Switching from red machines so trying to grasp the deere systems. Thanks.

9770sts head