Contact busoni@poloniex, he handled the transfer and should be able to do it for you. Just keep in mind that any coins (earned pos), after the date of the transfer will not be credited.

That was the only exchange where they were added, and was the only "neutral" and "trustable" entity to handle the conversion.

Not sure the old dat file works in the new wallet anyways. I am sure it is not the same seed or addresses. Hope you have a copy of your wallet.dat file, I am not sure if the new wallet data is going to mess it up (corrupt it), if you try to later read it with the old wallet.