I found some at a large oil depot in a 5gal bucket. Used/ing it in my A and changed out my 38'pu. On the 38pu I changed the transmission gear oil back to 90-140 as the other was so thick that downshifting was a more difficult then compared to the lighter weight oil.
If you want a bunch of good info from people here on 600w...
http://fordbarn.com/forum/showthread.php?t=9550