I am by no means an expert at this, but just finished installing a used engine in mine. Junkyard motor w/ 88k on it. Purchased from Rockford Auto Parts in Chicago, came with a 90 day warranty.
I probably voided the warranty, but went ahead and replaced the oil pump, rear main seal, motor mounts, crank sensor, and water pump before I put it in - just because.
Not sure if you have the option or leverage in your deal, but depending on the mileage of the used engine you may want to look at replacing some hard to get to items while its out.
By the way, its only been one day, but the engine runs great, so I would not have any reservations about a low mileage used replacement.