Running engine apart is probably the better way to go, but beware the "pile of parts" engine that has never been assembled unless you're a builder yourself. Wrong parts, wrong clearances, no history marks to see how it was put together or signs of potential problems.

If you can, get the manufacturers part numbers from the seller, as it may not be evident from looking at the parts. These can be really helpful when it comes to replacements or checking the manufacturer's instruction sheets to make sure things were done correctly.