The oil capacity for a 1997 Ford E350 diesel depends on the engine. Ford E-350s from that year could have several different diesel engines (e.g., 7.3L Powerstroke).
You absolutely MUST check your owner's manual. It will specify the exact oil capacity for your particular engine.
Trying to guess could lead to under-filling (damaging the engine) or over-filling (causing leaks and other problems). The owner's manual is the only reliable source for this information.
