You are a smart guy so I'm commenting more for others in the audience.
Just to be "Captain Obvious" I don't think I would pull an engine unless I could do a compression test on it.
That and the usual check the oil and look inside the valve covers if possible.
Some yards keep pretty fair records on mileage and what was good when the car was obtained.
Even the general condition of the car can tell you something about the way it was maintained.
If you see one with the whole side caved in it's pretty obvious why it's in the yard.
If it's still pretty much complete with no damage then likely something failed trans or engine.
There are actually fairly few pick a part type places around here anymore.
They used to be fairly common.
Excellent points.
When I used to look for an engine to clean up and put into immediate service, I did look close at the donor vehicle. A hard hit in the side or rear was a good indicator that the vehicle was operational when it was wrecked.
I would usually pull the spark plugs to look for oil burning. I'd pull the valve covers to look for sludge buildup. Finally, I'd look at a couple rod and main bearings. If it passed all those checks, it was usually a winner.
I'm leaning heavily towards an engine to rebuild so all I need is a solid core to build on.
I just was reminded that MDS engines are the 2005-2008 so that is my range of year models to pick from.
I've been price shopping the "stroker" kits and what was around $2000 a few months ago is now either unavailable or around $3000 now.
If by some strange chance I come across a 2005-2008 engine with under 100,000 miles, I might just pull the heads to have my guy correct any valve seat problems, then run it as is. To do that, I'd need a full service wrecking yard. I haven't figured out how to determine the mileage of a vehicle in the self serve yards since they pull the batteries and the odometers are electronic.
Spending $2000 on a low mileage engine, machine work on the heads (and TTY bolts) and head gaskets might be an option to consider.