Al,
Not with this car, but if you go back to The Star Magazine, last year I wrote an article on Satish Tummala of Motorwerks, and in the article is mention of his W126 conversion to V12.
He had a local place here custom fabricate an aluminum radiator because the stock one would no longer fit.
I don't know which shop he used, but there are many custom radiator fabricators around these parts, the land of custom rods. I did a quick search and found about 4 local--that's without any effort.
The photo of his engine bay is the lead photo here:
http://www.mbcoupes.com/w126index.htm