Long vs shortbed is really just personal preference.
In OPs case, if considering a truck that needs major work or replacement to virtually every panel and half the cab, turning a long bed into a short bed is just another task on the list and $500.
You have to be not worried aboot cutting, hacking, welding, drilling, bondo, time and motivation if you’re getting into a major rust/bodywork job. That’s where a long to short conversion makes the most sense imo. Less so than on a clean straight good condition truck. Again JMO.