Did something illegal happen here?

I bought a '91 Ford F-250 4x4. Frank, the guy I got it from, bought it from the local school district. The truck was built with a 5.8 liter engine, which was the smallest available in that model. I believe Frank thought it had a 5.8, because he used spark plugs for a 5.8 engine. I discovered that it has a 5.0 in it. It's a non-driveable pile because of this. I suspect that a school district mechanic had a 5.0 Mustang and decided to swap the two engines. Wouldn't that amount to theft? I know Frank and I both bought it as-is, but neither of us was told it had the wrong engine.

Read more: Did something illegal happen here?