I have a world with dozens of chests. They are filled with piles of every conceivable crafting item and ever weapon, accessory and armor possible.
In my mind I see each item being converted to its 1.3 counterpart by careful consideration by a council of Ents.
Still stuck at 75%. I guess I will just walk away and come back tomorrow, but I fully expect to see 75% upon my return. At that point I will reboot expecting to see my save files have been corrupted. I will delete and start over.
I was planning on a fresh start in a new world, but it will be a real shame to lose all of the cool and unique structures that I have built with my son over the last few years.