That is a nice looking old guitar.
You might want to oil the fretboard with some lemon oil or something and get some strings on there so that neck has the right tension on it. I imagine you have the bridge and tailpiece.
I don't believe it is good to let a neck sit without strings on it. It might get a mind of its own and decide to do its own thing, much to your consternation.
Hopefully it has not sat without strings for a long period of time.
I usually even change strings one at a time, and tune each one roughly up so that the neck retains the same fundamental tension on it. On a difficult to notice level the neck changes its orientation from being tensioned by the strings to being totally untensioned. Hopefully it will move back into the correct orientation when it gets retensioned.
I'm not sure how true this concept is, but I believe it to be correct and I stopped removing all the strings at one time when restringing because of this theoretical characteristic.
I'm not trying to tell you what to do, it's your guitar - you can do whatever you want with it. I'm just sharing something I heard, and realize you are probably cleaning or replacing the parts and have every intention of stringing it without much delay.
I think that is a real nice looking Epi, worth fixing up. It's definitely not a model I've ever seen.