All doors, including cargo doors on the 727 are plug type doors.
Thanks for the info on the DPSI when that occured, but that statement there is incorrect, the right side cargo (pit) doors are hinge type doors which open outward (except on certain 727-200s which had 3 cargo doors in which the aft one is a plug door). The cargo converted 727s I fly all have hinge type main cargo doors which lock into place with 6 big locks on the bottom and (I believe) 5 camlocks along each side.