* 7.5L (460 cubic inch) V8: This was a very popular and powerful gasoline engine.
* 6.9L (420 cubic inch) IDI Diesel: This was a naturally aspirated diesel.
* 7.3L (445 cubic inch) IDI Diesel: A slightly larger displacement version of the 6.9L IDI diesel.
To know for certain which engine is in a *specific* 1989 Ford F-350, you'd need to check the vehicle's documentation (like the owner's manual or title) or look at the engine itself for identification markings. The engine code will be stamped on a visible part of the engine block.