Thanks. Your observations about the grapple are spot on. This current design fits flush onto the angled top plates of the standard dreadnought torso. My thought was that it's powered by some sort of strong "gravitic plating" (or similar sci-fi hand waving --like an enormous electromagnet).
At the moment, I'm not really sure what alternative I should go with. A more claw-like system would be unlikely to fit the unusual angles on the dreadnought very well, but maybe I'll use something like that anyway. Since it'll never actually hold a dreadnought, all it has to do is
look the part.
I just don't really like the ungainly looking systems that they designed for the or the with long, spindly arms gripping the cargo from the sides. It just looks improbable from an engineering standpoint --and not in a cool way --which is usually my 40k litmus test since so many things defy the laws of rationality.
Oh well, I mull it over while I work more on the rest.