I don't know if you are a lucky guy or not, I own several engines and most of them are in their original boxes some of them with ATF and some not, like you I have used some of those engines years after and I just use a new plug and they start right away. The ATF is so cheap that I try to use it so often, been the commonly that I sometimes forget to use it as an after run oil but my honest advise will be: Use ATF and like someone else said it before, plug all the engine's holes and place it upright and forget about it, when ever you will use it again just drain the ATF and place a new plug it will start like it is doing right now.
Alfred