Excavation could provide evidence for the movement or non movement of stones . The cairn is likely to have followed the erection of the structural stones and their sockets would be self explanatory . There is also the possibility of a revetment and any disturbance to that would also provide info of possible movement of stones but the sockets would be the most informative .

Roy , I foresee problems if there is no proof and “obvious “ is only subjective .
I get the impression that you will suggest that one stone (I know you said earlier that four were moved but one is enough to illustrate the hypothetical problem ) was moved from it's original position to replace another dislodged ? stone and in turn be replaced by another . It cannot be obvious which of the original stones was moved as you don't know and cannot know without evidence that it was ever there .If it had a distinctive profile which matched an excavated socket you could then prove it but there is no basis for believing a particular stone was anywhere without proof you can only suggest it and from there continue on to the movement of the other , equally problematical three . The basic problem is that to produce what is obvious to you , you have to have an ideal model of the original that without proof derived from excavation only exists in your head and which you cannot prove ever existed .