Engines were meant to be run, not to sit. With no gas and air and oil constantly moving through the different parts, things can get stuck and gummed up. I'd fully prep it if I planned on letting it sit for a while.
If their is no oil in it, and the hole is open to the air, then yes you will get damage. It will rust the internals and maybe cause pitting due to the fact that air has moisture in it. if the garage is heated you should be fine. I would do something to cover the hole.
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