ideally you want to hear the engine running, buying a second hand engine is a gamble really unless you have full documented history with it.
Visual checks and and possibly a compression test are all you can carry out with the engine out of the car. Check for oil leaks, missing sensors, condition of belts, pulleys, exhaust manifold etc etc etc.
I was recently in your position, and now have the 48k replacement engine fitted and running and im very happy with it. So many worries came to mind though, thats why most people goto Joe at country cruising, for engines and fitment etc, for that peace of mind.
You probably know all above as you've had coupes previously, but i hope info helps anyway, and good luck!
Rob.