I'd vote for an old pickup truck too! Most car models would look noticeably dated (although there were plenty of 1980 model cars still on the road in 1997; it wouldn't be hard to acquire one, but it would definitely look like an old car.) Pickup truck just reads as "pickup truck" to most people though, and they tend to be driven around a lot longer, so a 20-year-old one wouldn't stand out at much.

Alternatively, a white panel van.