It should have nearly new belts in it, or else need them. There are cast gears on the side which run in the open, they are about due to be replaced.  Look the pickup attachment over well, especially the cams on the ends which control the teeth.  That is about where we rebuilt them on ours.  The net knives require periodic replacement or very fine sharpening. 

We've run a 664 since '97 and it's been a good baler.  Had a  bit of a fire problem last week with it.