To switch to the entire HO package, you'll need, well, the entire HO package. The complete wire harness (even under the dash). If you can get a donor vehicle, it's pretty straight forward. It's been done before. :thumbsup:
If you don't want to swap out the entire harness and dash, but you need an engine, top to bottom, I'd keep looking for a Renix-era truck that has exactly what you're missing.