Advice on buying junkyard engines?

I would rather buy a known good motor with no warranty from a running vehicle or buy the whole vehicle than buy a used motor with a warranty that I can't test run and pressure test the cooling system.
Sometimes you have to buy the whole buffalo to get a good motor.
In this area $1000 gets a beat to stink mid 90s truck with a good 100/150k magnum motor in it.
The best ones come from the church vans.