Thanks for the pictures. You made a good point about the heavy trucks I didn't think of. Attached is a link to a 1956 Ford truck listing showing they used a 272 in the F600 and F700 big trucks with a Holley 4000G (Governor). They used manual chokes, so no need to drill the intakes for choke heat. I think you just hit the nail on the head and solved the mystery.
Sal
http://www.thecarburetorshop.com/Tru...F.htm#TkitFord