You best make sure you have a really strong tranny. Most old combines arn't made to push or pull, well the new ones aren't either. That combine ins't going to be able to do much pushing either, it'll grade your driveway and thats about it.
What might be a better idea would be to try to mount a snowblower on the front instead, especially if combine is a hydro. You could use the header drive to run it.
i think that would be a good idea.... especially the snowblower idea i cant see either pushing any harder than my 8row 30" and 300+ bushels of corn do while running up a hill at 6mph