I don't know how one would ever be able to adjust the inboard/outboard position of the door if that deep bolt were in place.
I have never seen a bolt in that hole in any of the several trucks which I have taken apart.
I think it's just a 47-48 thing. The body service manual mentions loosening the 4 cap screws for adjustment and you can just make out a bolt inside the pocket...
197-1948 Servicing Chevrolet Truck Cabs
