Thanks! So just download the newest version of core and swap in my wallet.dat file ?
That's what 2RobPet did when upgrading from Bitcoin core v 0.8.3-beta. He also used the old blockchain files from v 0.8.3-beta in the latest version of core to save time syncing, and said it worked.
Solved it. Updated bitcoin core to the latest version, set the data directory to the same as my old version so I didn't have to redownload the blockchain, then cancelled the transaction with the abandon transaction function. Transaction sent and confirmed now.