* Small-block V8s: These were likely 302 cubic inch (5.0L) or 351 cubic inch (5.7L) engines.
* Big-block V8s: A 400 cubic inch (6.6L) or 460 cubic inch (7.5L) V8 were also options, though less common than the smaller V8s.
* Inline-6: A 400 cubic inch (6.6L) inline-six-cylinder engine was also available.
To know the *specific* engine in a particular 1978 Ford F-250 Custom, you'd need to check the vehicle's identification number (VIN) or look at the engine itself for identification markings.