The Starwagon is a mid engine arrangement. The Space Gear is laid out with the engine in the front. Have you ever watched "Dr. Who"? Do you remember the Tardis? There's a legend that the Starwagon design was influenced by and possibly related to the Tardis, from Dr. Who.
There are benefits to the Space Gear, for one you can comfortably pass from the cockpit to the rear cabin. In the Starwagon you can but you'd be crawling, just easier to get out so you don't need to crawl over the engine compartment. Go look at the technical drawings (shop manuals) in the L300 & L400 Dedicated Category Reference Forums in Delica Canada Technical. There are Long Wheel Base Starwagons, we just tend not to see as many in this neck of the woods.
Falco.
Good Ship