Ken:

The guys who ferry light aircraft around the pacific have a source of winds aloft prediction which works very well for them.  I believe the prediction is in knots plus or minus which makes it easy to plan your fuel requirements.

Dont know where this info is available but you might contact Aerolloyd at (321) 268-9692 Ext. 3107. or one of the other ferry services. 

Also you might contact Jon Johanson in Australia.  He has done it several times in an RV-4.  You can find him on the net.

Hank Huddleston