If you want Furnace, you need character level 31, to reduce the number of possible outcomes from upgrading rare to legendary (you exclude only Schaefer's and Athskeleng but who cares, pool of 4 is better than pool of 6).
This season I tried ~50 upgrades on my lvl70 char and got pretty frustrated due to fails.
Then I made new char, and first 2h mace I upgraded from rare to legendary was The Furnace. Crappy one, but it doesn't matter, I needed it only for cube.
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Im guessing they must have got them before this current patch?
I do have the Falcon WIngs but not Cosmic wings as yet.. a shame that, would have liked to have got those from Adria