Thought I would post more information that I found researching the Mopar modification in two service bulletins concerning shudder in 1978 era A904s with locking torque converters.
The kit mentioned in my original post is long gone, no one has it in stock. The part number of the spring is 4202672 and can be found sporadically. It is in both bulletins for lockup shudder. Harder to find is the vented lock up body, its part number is 4302209. It was in the second bulletin.
A workaround is the TF-TC shift improvement kit. If you have the unvented lock up module, step 6 drills two small holes that accomplishes the same thing bleeding off pressure.
Step 10 replaces the spring in the lock up module that is the subject of both of the bulletins, including the vented lock up module not modified in step 6.
The rest of the kit addresses the other common ills. I think I will go with the TF-2 kit for the rest and will just do the TF-TC mods for the lockup shudder raising the lockup to 40 Mph. It comes with some nifty drill bits for other uses.
Hope this helps someone out.
Craig