you need to make sure there is no rust or anything even if it was covered. most motors you buy used sit but are usually inside and certain things are plugged to prevent any stuff from getting in there. if the plugs were left in it then thats 4 holes that were covered. it never hurts to check it out first. on a hatch i had i got a motor from pull a part with 111k miles on it. it sat indoors for a few months before dropping in. with it being out of the car if you have a repair manual and the right tools it won't take long to check it out and then i would do new headgasket and other seals and belts before dropping it in. how bad did the other motor overheat? if it wasnt that bad then the motor is prob still good.