Wind instability is endemic with Vanagons but can be minimized:
* use stiff side walled tires - 8 ply on syncros - Yokohama Y370 LT 195/75R14
are good.
* balanced air pressure - very important especially in front - too low and the
front squirms and too high and the wind wins. Something around 43 lb. in front
should be ok.
* shocks up to snuff
* steering linkage at spec.

my 2 pfennigs
Larry
'86 Syncro Westfalia