The main advantage of the Herald as a cargo aircraft over the 748 and the F27 was the very large double doors with the low sill located aft.
The forward freight doors were tricky due to prop damage caused by the forklifts.
One snippet of useless information, the Herald had the two rear doors, the forward one as a passenger door, with the rear one opening to give access for cargo loading. Additionally there was a forward crew door, left hand side behind the cockpit, one of the original customers was an Australian airline who specified that the forward door opening should be designed to permit the loading of a standard bale of wool, this was incorporated into the design, the airline did not then buy the aircraft.
The pressurisation was pretty poor on the Herald, max diff 2.2 psi if you were very lucky, the large rear doors used to leak very badly, one regular load was a consignment of day old chicks that we used to fly down to Valencia, in order to prevent the chicks from expiring the flying spanner had to take a bin bag of wet rags on the trip and caulk the gaps around the doors to reduce the leaks. On the return trip we often brought back exhaust pipes for the Ford plants at Cologne and Speke.