Fiat/Bartoletti 642 N 2 Race Transporter in Maserati colors.
There was one
at auction on eBay, ended October 21, 2001. Opening bid $89.99, Buy It Now for
December 17, 2003: these are proliferating, and the price is coming
down. I tried to buy a yellow one, and a "classy Dk gray" one, but was
a day too late.
Michael T. Lynch's American
Sports Car Racing In The 1950s book has a couple of photos
of what may have been just such a vehicle (or its close relative)
before Lance Reventlow got his hands on it. Go to the "Photos"
page and look at the two in the bottom row of thumbnails.
There are some other photos of transport vehicles
on Al Long's site,
among many other interesting images, and a thread with many more leads to such,
F1 Nostalgia Forum.