* Wheelbase: Longer wheelbases generally allowed for higher GVWRs.
* Engine: Different engines had different weight capacities.
* Options: Things like heavier-duty suspension packages, added features, and even the number of passenger seats would impact the GVWR.
To find the GVWR for a *specific* 1984 Ford E350 Super Duty passenger van, you need to look at the vehicle's certification label (often called the sticker or placard). This label is usually located on the driver's side doorjamb, or sometimes on the glove box door. The GVWR will be clearly stated on that label.
