The bottom pic is the clearest exposition of your concept. By my onscreen measurement, the wheelbase discrepancy is 94%. The discrepancy in wheel diameter is 88%. Imagine a mannequin into the driver's seat. The windshield header will be coincident with the driver's forehead. But enough about the details.
There are things that are hard to move on a car body, like the cowl height and beltline. That's why you see show cars that are sectioned or have a chopped top, but what you don't see as much are slab sides and beltlines resculpted as you show.
Try this: Start with the stock Previa body and apply a slant chop. The stock roofline's highest point is over the middle seats. Essentially you would cut a slit across the top of the windshield and take 6-8" out of the rear posts. The rear seat disappears and the middle seat moves down and back (else a shag carpet and water bed interior).
The roof could follow Thee Holy Template which would gain a lot of cred on Ecomodder. I would then graft in the rear hatch from a Dodge Magnum since I rilly dig those. The aggressive fender flares could be body-kitted over the slab sides.
You could start the slant chop at the bottom of the windshield, but good luck with that.
Edit: Oh, my. You could have started over fresh at Ecomodder, but you posted that VWVortex thread. They're not very polite to you there, are they?
So the way I get it is that you are living in the Previa in question, with a CNC router taking up the whole back end. Is that about it?