I use Everclear to make my Triple Sec, also use Vodka in the recipe but with different fruit. The Everclear with the higher octane seems to pull the flavor out of oranges and other fruit better than Vodka. It is not the proof you are wanting out of it, at least for me, it is the ability to pull flavor and not add the wrong flavor. Once you add all the other ingredients the proof comes down.

Not a Lemoncello fan so other than that can not comment on the recipe.
Cheers,
T