Duno if it applies in the states....but I swapped cabs off of my 76 gmc onto another 76 gmc and went for inspection and they had big concerns why the vin numbers off the cab didnt match the frame.
just something to consider
if you have all the paper work you can have a new vin put in the door jamb no biggie
i removed my long bed all by myself once ..
unbolted it and tipped er to the side with out falling over
then pulled truck forward . let box down and yeepee..