Transits all used to be "big", since the 70s. Then recently they made a small van, and just called it a transit...
All marketing. The big real transits actually come in a multitude of sizes and configurations. From box vans, with sliding tailgate, and high top panel vans with extra length down to pretty small vans.
They are mostly used for minibuses though rather than personal transport in the disabled market. A small rear drive minibus like here:
http://www.ford.co.uk/Commercialvehicles/TransitMinibusCheck out the different options, sizes, chassis cabs, Front, rear, or 2 or 4 wheel drive, etc. Bit big for private use.