I have the center plate for a B&W turn over ball hitch and will fabricate my own crossmembers/brackets for my 6400.
A 3600 might not have enough springs back there to take much hitch weight from a gooseneck, certainly not like the present day pickups do.
Please elaborate on the tag along hitch you found for the 3600.
Years ago I found one perfect for my 3800 (and then moved it to the 6400) but never knew the intended application to get another. The frames on these AD trucks 3/4 ton through 2 ton are 36" wide outside. Most modern stuff is 34", so most hitches don't fit easily.
