1) One thought:
You could certainly keep your 16" wheels, and simply get a new 16" tire size that has shorter sidewalls. This would accomplish the same thing as getting new, smaller wheels and tires....but would save you the money you would have spent on new wheels.
With a slightly smaller outer diameter on your tires, the odometer and speedometer will indeed "read a little bit high," but the van ought to drive just fine. If you are absolutely determined to make your speedometer/odometer as accurate as it can be, it is possible to recalibrate your speedometer module yourself pretty easily.
This video below covers what's involved.....
(*The video says its for 1992-1996 Broncos and F-series trucks, but the Econolines of the same years have the same speedometer module....I used this video to learn how to recalibrate the speedometer in my '95 E250 after I went to taller tires.)