From Hemmings yesterday:
"A more typical cabover engine choice might be the GMC Twin Six V-12 of the 1960s, one of the last attempts to wring as much power out of gasoline engine packaging for big trucks before the era of diesel took over. Mac’s Motor City Garage has more on the unusual engine."
http://www.macsmotorcitygarage.com/2...ubic-inch-v12/
Some of the comments below the article aren't too complimentary. Several good ones though, especially the one at the bottom from Zorba.