Engine Replacement or Rebuild

My Son's 04 RSX Base, AT, 180K miles has a blown head gasket more than likely due to it overheating a few months back. We can get used engine with 100K miles on it locally for $600. We've had quotes for repair/rebuild about $1200. Was thinking about a DIY project but haven't tackled anything like this.

Any suggests on a direction?

Engine Replacement or Rebuild