I've thought about this before for the primary benefit of being able to
leave the windows open an inch or so to ventilate the locked van in the
summer without someone being able to pop the door locks with a piece of bent
coat hanger. 

However, if you do this swap the gap in the glass overlap faces forward, and
at road speed in the rain it's likely that water will enter, and road noise
will be even worse, though that's hard to imagine.  It could even degrade
the perfectly horrible aerodynamics a bit!  

It's easy to do this swap with a bit of care on removal, and a greased 1/4
inch rope for installation, so I might try it next summer.  What I would
really like though is a set of jalousie (flip up) windows like my '68 had!

Stuart MacMillan
'84 Westy w/2.1
Westy owner since '74, but there are no more. :-(