I think a little time travel would be in order. I know the only way I could get the same gauge easily, even if I knew what size needle I used, would be to go back to that time to discover the frame of mind and mood and the "feel" in my hands that I had the day it was done.
If it was me facing this issue, I think I would forget trying to figure what size needle I used then but look to more recent projects on similar yarn for clues, make some educated guesses and swatch until I was blue in the face. Then when I got close, I'd try it and see on the project how it went and go up or down as needed.
You may find that no needle will give you the size you need without also adjusting the feel of the work in your hands to something a little different than what you do now. It can be a nightmare. If that is any encouragement. LOL