The old GMC V12s. They were based off of what was a 305 CID V6 series basically 2 stuck together. The 6es were available in up to 478 CID while the 12s were something like 700 CID if I remember correctly.
There was truck running around in Victoria BC with one of those in it, stock.
It was cool old truck, i had a long look at it parked outside the unemployment office about 10 years ago.
Seen it on the streets a few more times too.
Gary, That would be a great engine to use for a mid engine van mod...
[youtube]http://www.youtube.com/watch?v=puJaDfB4UFM[/youtube]
[youtube]http://www.youtube.com/watch?v=KU1lV7Qk ... r_embedded[/youtube]