Take a look at:-
The tutorial describes using the healing brush and content aware fill to remove power lines. Seems to me that it would hide the cracks in the scan.
The lines from one piece wouldn't line up with the others. Therefore, you would remove the crack, but anything continuing from one piece would not match another.
I was thinking that there would be a way to outline one piece and 'nestle' or 'nudge' it to another.
But, if anyone has a better idea, that would be great....
How about selecting the piece that doesn't "fit" on to a new layer. You could then free transform to move/nudge/rotate it until it gets to the best fit. At worst if the parts are too close together to select separately you could re-scan. How big is the file? Could you send it as an attachment? If so I'll see what I can do wit it.