John,
I don't have any experience with this subject, so I will just throw this out as a thought...
In my mind the tractor should be tied town with four chains, and then the implements should be secured with additional chains.
It seems like from what I can see in your photos that you are doing double duty with your chains. They are both holding the tractor and the implements...
I would not be comfortable doing this myself...but it could just be because I don't know better.
I would probably use four chains for the tractor, each which would go directly to tie points on the trailer, and additional chains to hold the implements.
My worry would be as you have the tractor chained down, with the chains running over the implements, that this could give additional opportunity to slack to develop in the chains as time passed when you were on the road...