I've not driven a Vanagon with only a large aftermarket front sway bar.
My Vanagon under steered pretty badly with stock suspension and stock
tires.  With the suspension and tires I indicated (and an EJ25 Subaru)
mine has very balanced handling.

I believe the ambulance model came with the rear sway bar shown in the
link below.  The part number for this rear bar is also indicated for the
front in some models.

http://www.oemepc.com/vw/part_single/catalog/vw/markt/RDW/modell/T2/year/1
986/drive_standart/65/hg_ug/511/subcategory/56000/part_id/3705862/lang/e