My problem with the WEG plan was the cargo hold left no room for engines! The huge exhausts on the aft quadrant seem to indicate a huge area taken up by the engine.

Yeah, that is a problem with it. But that is something of a problem with ALL Star Wars ships. Since technology in SW is essentially magic with tech sounding words attached I just assume that the nuts and bolts of the engine can be located elsewhere. Besides, SW engines are frequently very small in relation to the ships they drive, TIEs for example (star destroyers excepted, of course).