Pull the head.

If you're thinking of buying a motor, replacing a head gasket shouldn't be too much work, especially if you've got the motor on a bench.

Pull the head in the salvage yard, check out the bores and valves, if everything looks good put the head back on and buy the motor and replace the cam belt, tensioner, and head gasket, and you're golden.

This is assuming that it's the kind of salvage yard where you can pull the head prior to buying. If not the best you can do is spin it by hand in neutral and with no plugs and see how it feels...

Better safe than sorry. If you can't fully inspect it, wait until you find the cherry motor.