Normally, you send the engine and prop away for overhaul and refit them on completion. Count on a month to turn them round. There's always the possibility of a prop being out of limits and a replacement would make a fair dent in your beer money. So, part-used is an option. Whatever you do, don't buy anything without documentation ('Serviceable' label and log book) because your maintenance organisation won't (aren't allowed) fit it.