Heard from Dean Brasseur again. I had asked to buy a Legacy part to see if it could be modified back. Here is his response:
I am sorry, the Vision truck sides will not fit on these.
So, Lionel is not your solution. They have in effect washed their hands of this, but have no heartburn with us copying the JLC part.
Next step: I need to get my mitts on one of these castings that can be cut. One that is warping slightly but not crumbling would be best. Bob Stevenson is ready to make molds and do a "proof of concept" cast.